How do I read line by line in a file using while loop, and in each iteration, grep each line to compare to a...
up vote
2
down vote
favorite
I have a file called abc.txt with the contents as follows:
1: It is a shell script
2: There are few lines in this file
3: I am good with programming in C, but beginner in shell
4: We are going towards end of file
5: END OF FILE
I want to read each of the file iteratively, and in each iteration I want to compare the line with "I am good with programming in C, but beginner in shell", and then do some processing.
Any help would be greatly appreciated. Thanks!
command-line grep
asked Dec 4 at 17:32
ShellyBelly
656
add a comment |
up vote
2
down vote
favorite
I have a file called abc.txt with the contents as follows:
1: It is a shell script
2: There are few lines in this file
3: I am good with programming in C, but beginner in shell
4: We are going towards end of file
5: END OF FILE
I want to read each of the file iteratively, and in each iteration I want to compare the line with "I am good with programming in C, but beginner in shell", and then do some processing.
Any help would be greatly appreciated. Thanks!
command-line grep
asked Dec 4 at 17:32
ShellyBelly
656
add a comment |
up vote
2
down vote
favorite
up vote
2
down vote
favorite
I have a file called abc.txt with the contents as follows:
1: It is a shell script
2: There are few lines in this file
3: I am good with programming in C, but beginner in shell
4: We are going towards end of file
5: END OF FILE
I want to read each of the file iteratively, and in each iteration I want to compare the line with "I am good with programming in C, but beginner in shell", and then do some processing.
Any help would be greatly appreciated. Thanks!
command-line grep
asked Dec 4 at 17:32
ShellyBelly
656
I have a file called abc.txt with the contents as follows:
1: It is a shell script
2: There are few lines in this file
3: I am good with programming in C, but beginner in shell
4: We are going towards end of file
5: END OF FILE
I want to read each of the file iteratively, and in each iteration I want to compare the line with "I am good with programming in C, but beginner in shell", and then do some processing.
Any help would be greatly appreciated. Thanks!
command-line grep
command-line grep
asked Dec 4 at 17:32
ShellyBelly
656
asked Dec 4 at 17:32
ShellyBelly
656
asked Dec 4 at 17:32
ShellyBelly
656
asked Dec 4 at 17:32
ShellyBelly
656
asked Dec 4 at 17:32
ShellyBelly
656
656
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
up vote
7
down vote
Using a shell loop is unnecessary, as grep already iterates over lines:
grep '^[0-9]: I am good with programming in C, but beginner in shell' input.txt
If there's a matching line, it will be printed. [0-9] defines range of characters that will be matched. We can also extend that to longer numbers [0-9]*: (and I think with perl regex -P option that could be done as [0-9]+:).
If a shell loop is really necessary, we can use case statement for pattern matching
while IFS= read -r line; do
case $line in
*": I am good with programming in C") echo "Matched: $line";;
esac
done < input.xt
edited Dec 4 at 19:21
dessert
21.7k55896
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
^[0-9]:isn't needed at all either, it seems.
– Michael Hampton
Dec 5 at 3:01
@MichaelHampton To be fair, yes, in this case not needed at all - user can get away with just.*I am good with programming in Cor just pick a unique word from that sentence. Or evengrep 'C.*shell'. There's no and statement in grep, but we could get away withgrep 'shell' | grep 'C'. Of course, everything depends on user's input data to construct a proper regex pattern.
– Sergiy Kolodyazhnyy
Dec 5 at 4:48
@SergiyKolodyazhnyy, See this question, this is exactly what I need. Please help! askubuntu.com/questions/1098503/…
– ShellyBelly
Dec 5 at 20:35
add a comment |
up vote
7
down vote
Try this sample code to help identify and modify to suit your needs:
#!/usr/bin/env bash
set -e
set -x
while read -r linenum line
do
if [ "$line" = "I am good with programming in C, but beginner in shell" ]
then
# Process things here
echo "same"
fi
done < "$1"
Usage:
Make executable:
chmod +x script.sh
Place script in any folder then run script by passing a file to it:
./script.sh /path/to/data.txt
Info:
-r: Option passed to read command prevents backslash escapes from being interpreted.
set -e: Bash option to stop script on first error.
set -x: Bash option used to debug the scrtip.
"$1": The file variable passed to the script in this casedata.txt
linenum: variable that holds the line numbers when bash splits the read lines into two variables while the other is passed in via thelinvariable.
answered Dec 4 at 18:03
George Udosen
19.1k94266
1
@George So you're using-d" "to split on whitespace and cut all lines starting from the second one. I'd suggest another way:while IFS= read -r linenum line. The shell will perform wordsplitting on the input line and place first item ( line numbers ) intolinenumvariable, but all other things will go intolinevariable. Aside from other things,casestatement can be used as alternative to[[comparison.
– Sergiy Kolodyazhnyy
Dec 4 at 18:44
Can I implement this script in #!/bin/sh ?
– ShellyBelly
Dec 4 at 18:49
@AkshayNandi Yes, but you need to change[[to[because[[is specific tobash. See my answer for portable solution
– Sergiy Kolodyazhnyy
Dec 4 at 18:52
@SergiyKolodyazhnyy I tried that it didn't do so on the word splitting.
– George Udosen
Dec 4 at 19:36
1
@GeorgeUdosen Ah, yes, I found the issue - it's because ofIFS=. It unsets the variable temporarily, which is what is used for word splitting.IFSdefaults to whitespace,tab,and newline. And it's a habit, but also for a good reason, to unset it - if there's a leading whitespace ( line starts with space ) it would be gone withoutIFS=
– Sergiy Kolodyazhnyy
Dec 5 at 0:07
|
show 2 more comments
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
7
down vote
Using a shell loop is unnecessary, as grep already iterates over lines:
grep '^[0-9]: I am good with programming in C, but beginner in shell' input.txt
If there's a matching line, it will be printed. [0-9] defines range of characters that will be matched. We can also extend that to longer numbers [0-9]*: (and I think with perl regex -P option that could be done as [0-9]+:).
If a shell loop is really necessary, we can use case statement for pattern matching
while IFS= read -r line; do
case $line in
*": I am good with programming in C") echo "Matched: $line";;
esac
done < input.xt
edited Dec 4 at 19:21
dessert
21.7k55896
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
^[0-9]:isn't needed at all either, it seems.
– Michael Hampton
Dec 5 at 3:01
@MichaelHampton To be fair, yes, in this case not needed at all - user can get away with just.*I am good with programming in Cor just pick a unique word from that sentence. Or evengrep 'C.*shell'. There's no and statement in grep, but we could get away withgrep 'shell' | grep 'C'. Of course, everything depends on user's input data to construct a proper regex pattern.
– Sergiy Kolodyazhnyy
Dec 5 at 4:48
@SergiyKolodyazhnyy, See this question, this is exactly what I need. Please help! askubuntu.com/questions/1098503/…
– ShellyBelly
Dec 5 at 20:35
add a comment |
up vote
7
down vote
Using a shell loop is unnecessary, as grep already iterates over lines:
grep '^[0-9]: I am good with programming in C, but beginner in shell' input.txt
If there's a matching line, it will be printed. [0-9] defines range of characters that will be matched. We can also extend that to longer numbers [0-9]*: (and I think with perl regex -P option that could be done as [0-9]+:).
If a shell loop is really necessary, we can use case statement for pattern matching
while IFS= read -r line; do
case $line in
*": I am good with programming in C") echo "Matched: $line";;
esac
done < input.xt
edited Dec 4 at 19:21
dessert
21.7k55896
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
^[0-9]:isn't needed at all either, it seems.
– Michael Hampton
Dec 5 at 3:01
@MichaelHampton To be fair, yes, in this case not needed at all - user can get away with just.*I am good with programming in Cor just pick a unique word from that sentence. Or evengrep 'C.*shell'. There's no and statement in grep, but we could get away withgrep 'shell' | grep 'C'. Of course, everything depends on user's input data to construct a proper regex pattern.
– Sergiy Kolodyazhnyy
Dec 5 at 4:48
@SergiyKolodyazhnyy, See this question, this is exactly what I need. Please help! askubuntu.com/questions/1098503/…
– ShellyBelly
Dec 5 at 20:35
add a comment |
up vote
7
down vote
up vote
7
down vote
Using a shell loop is unnecessary, as grep already iterates over lines:
grep '^[0-9]: I am good with programming in C, but beginner in shell' input.txt
If there's a matching line, it will be printed. [0-9] defines range of characters that will be matched. We can also extend that to longer numbers [0-9]*: (and I think with perl regex -P option that could be done as [0-9]+:).
If a shell loop is really necessary, we can use case statement for pattern matching
while IFS= read -r line; do
case $line in
*": I am good with programming in C") echo "Matched: $line";;
esac
done < input.xt
edited Dec 4 at 19:21
dessert
21.7k55896
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
Using a shell loop is unnecessary, as grep already iterates over lines:
grep '^[0-9]: I am good with programming in C, but beginner in shell' input.txt
If there's a matching line, it will be printed. [0-9] defines range of characters that will be matched. We can also extend that to longer numbers [0-9]*: (and I think with perl regex -P option that could be done as [0-9]+:).
If a shell loop is really necessary, we can use case statement for pattern matching
while IFS= read -r line; do
case $line in
*": I am good with programming in C") echo "Matched: $line";;
esac
done < input.xt
edited Dec 4 at 19:21
dessert
21.7k55896
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
edited Dec 4 at 19:21
dessert
21.7k55896
edited Dec 4 at 19:21
dessert
21.7k55896
edited Dec 4 at 19:21
dessert
21.7k55896
21.7k55896
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
answered Dec 4 at 18:52
Sergiy Kolodyazhnyy
68.9k9143303
68.9k9143303
^[0-9]:isn't needed at all either, it seems.
– Michael Hampton
Dec 5 at 3:01
@MichaelHampton To be fair, yes, in this case not needed at all - user can get away with just.*I am good with programming in Cor just pick a unique word from that sentence. Or evengrep 'C.*shell'. There's no and statement in grep, but we could get away withgrep 'shell' | grep 'C'. Of course, everything depends on user's input data to construct a proper regex pattern.
– Sergiy Kolodyazhnyy
Dec 5 at 4:48
@SergiyKolodyazhnyy, See this question, this is exactly what I need. Please help! askubuntu.com/questions/1098503/…
– ShellyBelly
Dec 5 at 20:35
add a comment |
^[0-9]:isn't needed at all either, it seems.
– Michael Hampton
Dec 5 at 3:01
@MichaelHampton To be fair, yes, in this case not needed at all - user can get away with just.*I am good with programming in Cor just pick a unique word from that sentence. Or evengrep 'C.*shell'. There's no and statement in grep, but we could get away withgrep 'shell' | grep 'C'. Of course, everything depends on user's input data to construct a proper regex pattern.
– Sergiy Kolodyazhnyy
Dec 5 at 4:48
@SergiyKolodyazhnyy, See this question, this is exactly what I need. Please help! askubuntu.com/questions/1098503/…
– ShellyBelly
Dec 5 at 20:35
^[0-9]: isn't needed at all either, it seems.– Michael Hampton
Dec 5 at 3:01
^[0-9]: isn't needed at all either, it seems.– Michael Hampton
Dec 5 at 3:01
@MichaelHampton To be fair, yes, in this case not needed at all - user can get away with just
.*I am good with programming in C or just pick a unique word from that sentence. Or even grep 'C.*shell'. There's no and statement in grep, but we could get away with grep 'shell' | grep 'C' . Of course, everything depends on user's input data to construct a proper regex pattern.– Sergiy Kolodyazhnyy
Dec 5 at 4:48
@MichaelHampton To be fair, yes, in this case not needed at all - user can get away with just
.*I am good with programming in C or just pick a unique word from that sentence. Or even grep 'C.*shell'. There's no and statement in grep, but we could get away with grep 'shell' | grep 'C' . Of course, everything depends on user's input data to construct a proper regex pattern.– Sergiy Kolodyazhnyy
Dec 5 at 4:48
@SergiyKolodyazhnyy, See this question, this is exactly what I need. Please help! askubuntu.com/questions/1098503/…
– ShellyBelly
Dec 5 at 20:35
@SergiyKolodyazhnyy, See this question, this is exactly what I need. Please help! askubuntu.com/questions/1098503/…
– ShellyBelly
Dec 5 at 20:35
add a comment |
up vote
7
down vote
Try this sample code to help identify and modify to suit your needs:
#!/usr/bin/env bash
set -e
set -x
while read -r linenum line
do
if [ "$line" = "I am good with programming in C, but beginner in shell" ]
then
# Process things here
echo "same"
fi
done < "$1"
Usage:
Make executable:
chmod +x script.sh
Place script in any folder then run script by passing a file to it:
./script.sh /path/to/data.txt
Info:
-r: Option passed to read command prevents backslash escapes from being interpreted.
set -e: Bash option to stop script on first error.
set -x: Bash option used to debug the scrtip.
"$1": The file variable passed to the script in this casedata.txt
linenum: variable that holds the line numbers when bash splits the read lines into two variables while the other is passed in via thelinvariable.
answered Dec 4 at 18:03
George Udosen
19.1k94266
1
@George So you're using-d" "to split on whitespace and cut all lines starting from the second one. I'd suggest another way:while IFS= read -r linenum line. The shell will perform wordsplitting on the input line and place first item ( line numbers ) intolinenumvariable, but all other things will go intolinevariable. Aside from other things,casestatement can be used as alternative to[[comparison.
– Sergiy Kolodyazhnyy
Dec 4 at 18:44
Can I implement this script in #!/bin/sh ?
– ShellyBelly
Dec 4 at 18:49
@AkshayNandi Yes, but you need to change[[to[because[[is specific tobash. See my answer for portable solution
– Sergiy Kolodyazhnyy
Dec 4 at 18:52
@SergiyKolodyazhnyy I tried that it didn't do so on the word splitting.
– George Udosen
Dec 4 at 19:36
1
@GeorgeUdosen Ah, yes, I found the issue - it's because ofIFS=. It unsets the variable temporarily, which is what is used for word splitting.IFSdefaults to whitespace,tab,and newline. And it's a habit, but also for a good reason, to unset it - if there's a leading whitespace ( line starts with space ) it would be gone withoutIFS=
– Sergiy Kolodyazhnyy
Dec 5 at 0:07
|
show 2 more comments
up vote
7
down vote
Try this sample code to help identify and modify to suit your needs:
#!/usr/bin/env bash
set -e
set -x
while read -r linenum line
do
if [ "$line" = "I am good with programming in C, but beginner in shell" ]
then
# Process things here
echo "same"
fi
done < "$1"
Usage:
Make executable:
chmod +x script.sh
Place script in any folder then run script by passing a file to it:
./script.sh /path/to/data.txt
Info:
-r: Option passed to read command prevents backslash escapes from being interpreted.
set -e: Bash option to stop script on first error.
set -x: Bash option used to debug the scrtip.
"$1": The file variable passed to the script in this casedata.txt
linenum: variable that holds the line numbers when bash splits the read lines into two variables while the other is passed in via thelinvariable.
answered Dec 4 at 18:03
George Udosen
19.1k94266
1
@George So you're using-d" "to split on whitespace and cut all lines starting from the second one. I'd suggest another way:while IFS= read -r linenum line. The shell will perform wordsplitting on the input line and place first item ( line numbers ) intolinenumvariable, but all other things will go intolinevariable. Aside from other things,casestatement can be used as alternative to[[comparison.
– Sergiy Kolodyazhnyy
Dec 4 at 18:44
Can I implement this script in #!/bin/sh ?
– ShellyBelly
Dec 4 at 18:49
@AkshayNandi Yes, but you need to change[[to[because[[is specific tobash. See my answer for portable solution
– Sergiy Kolodyazhnyy
Dec 4 at 18:52
@SergiyKolodyazhnyy I tried that it didn't do so on the word splitting.
– George Udosen
Dec 4 at 19:36
1
@GeorgeUdosen Ah, yes, I found the issue - it's because ofIFS=. It unsets the variable temporarily, which is what is used for word splitting.IFSdefaults to whitespace,tab,and newline. And it's a habit, but also for a good reason, to unset it - if there's a leading whitespace ( line starts with space ) it would be gone withoutIFS=
– Sergiy Kolodyazhnyy
Dec 5 at 0:07
|
show 2 more comments
up vote
7
down vote
up vote
7
down vote
Try this sample code to help identify and modify to suit your needs:
#!/usr/bin/env bash
set -e
set -x
while read -r linenum line
do
if [ "$line" = "I am good with programming in C, but beginner in shell" ]
then
# Process things here
echo "same"
fi
done < "$1"
Usage:
Make executable:
chmod +x script.sh
Place script in any folder then run script by passing a file to it:
./script.sh /path/to/data.txt
Info:
-r: Option passed to read command prevents backslash escapes from being interpreted.
set -e: Bash option to stop script on first error.
set -x: Bash option used to debug the scrtip.
"$1": The file variable passed to the script in this casedata.txt
linenum: variable that holds the line numbers when bash splits the read lines into two variables while the other is passed in via thelinvariable.
answered Dec 4 at 18:03
George Udosen
19.1k94266
Try this sample code to help identify and modify to suit your needs:
#!/usr/bin/env bash
set -e
set -x
while read -r linenum line
do
if [ "$line" = "I am good with programming in C, but beginner in shell" ]
then
# Process things here
echo "same"
fi
done < "$1"
Usage:
Make executable:
chmod +x script.sh
Place script in any folder then run script by passing a file to it:
./script.sh /path/to/data.txt
Info:
-r: Option passed to read command prevents backslash escapes from being interpreted.
set -e: Bash option to stop script on first error.
set -x: Bash option used to debug the scrtip.
"$1": The file variable passed to the script in this casedata.txt
linenum: variable that holds the line numbers when bash splits the read lines into two variables while the other is passed in via thelinvariable.
answered Dec 4 at 18:03
George Udosen
19.1k94266
edited Dec 5 at 7:42
answered Dec 4 at 18:03
George Udosen
19.1k94266
answered Dec 4 at 18:03
George Udosen
19.1k94266
answered Dec 4 at 18:03
George Udosen
19.1k94266
19.1k94266
1
@George So you're using-d" "to split on whitespace and cut all lines starting from the second one. I'd suggest another way:while IFS= read -r linenum line. The shell will perform wordsplitting on the input line and place first item ( line numbers ) intolinenumvariable, but all other things will go intolinevariable. Aside from other things,casestatement can be used as alternative to[[comparison.
– Sergiy Kolodyazhnyy
Dec 4 at 18:44
Can I implement this script in #!/bin/sh ?
– ShellyBelly
Dec 4 at 18:49
@AkshayNandi Yes, but you need to change[[to[because[[is specific tobash. See my answer for portable solution
– Sergiy Kolodyazhnyy
Dec 4 at 18:52
@SergiyKolodyazhnyy I tried that it didn't do so on the word splitting.
– George Udosen
Dec 4 at 19:36
1
@GeorgeUdosen Ah, yes, I found the issue - it's because ofIFS=. It unsets the variable temporarily, which is what is used for word splitting.IFSdefaults to whitespace,tab,and newline. And it's a habit, but also for a good reason, to unset it - if there's a leading whitespace ( line starts with space ) it would be gone withoutIFS=
– Sergiy Kolodyazhnyy
Dec 5 at 0:07
|
show 2 more comments
1
@George So you're using-d" "to split on whitespace and cut all lines starting from the second one. I'd suggest another way:while IFS= read -r linenum line. The shell will perform wordsplitting on the input line and place first item ( line numbers ) intolinenumvariable, but all other things will go intolinevariable. Aside from other things,casestatement can be used as alternative to[[comparison.
– Sergiy Kolodyazhnyy
Dec 4 at 18:44
Can I implement this script in #!/bin/sh ?
– ShellyBelly
Dec 4 at 18:49
@AkshayNandi Yes, but you need to change[[to[because[[is specific tobash. See my answer for portable solution
– Sergiy Kolodyazhnyy
Dec 4 at 18:52
@SergiyKolodyazhnyy I tried that it didn't do so on the word splitting.
– George Udosen
Dec 4 at 19:36
1
@GeorgeUdosen Ah, yes, I found the issue - it's because ofIFS=. It unsets the variable temporarily, which is what is used for word splitting.IFSdefaults to whitespace,tab,and newline. And it's a habit, but also for a good reason, to unset it - if there's a leading whitespace ( line starts with space ) it would be gone withoutIFS=
– Sergiy Kolodyazhnyy
Dec 5 at 0:07
1
1
@George So you're using
-d" " to split on whitespace and cut all lines starting from the second one. I'd suggest another way: while IFS= read -r linenum line. The shell will perform wordsplitting on the input line and place first item ( line numbers ) into linenum variable, but all other things will go into line variable. Aside from other things, case statement can be used as alternative to [[ comparison.– Sergiy Kolodyazhnyy
Dec 4 at 18:44
@George So you're using
-d" " to split on whitespace and cut all lines starting from the second one. I'd suggest another way: while IFS= read -r linenum line. The shell will perform wordsplitting on the input line and place first item ( line numbers ) into linenum variable, but all other things will go into line variable. Aside from other things, case statement can be used as alternative to [[ comparison.– Sergiy Kolodyazhnyy
Dec 4 at 18:44
Can I implement this script in #!/bin/sh ?
– ShellyBelly
Dec 4 at 18:49
Can I implement this script in #!/bin/sh ?
– ShellyBelly
Dec 4 at 18:49
@AkshayNandi Yes, but you need to change
[[ to [ because [[ is specific to bash. See my answer for portable solution– Sergiy Kolodyazhnyy
Dec 4 at 18:52
@AkshayNandi Yes, but you need to change
[[ to [ because [[ is specific to bash. See my answer for portable solution– Sergiy Kolodyazhnyy
Dec 4 at 18:52
@SergiyKolodyazhnyy I tried that it didn't do so on the word splitting.
– George Udosen
Dec 4 at 19:36
@SergiyKolodyazhnyy I tried that it didn't do so on the word splitting.
– George Udosen
Dec 4 at 19:36
1
1
@GeorgeUdosen Ah, yes, I found the issue - it's because of
IFS=. It unsets the variable temporarily, which is what is used for word splitting. IFS defaults to whitespace,tab,and newline. And it's a habit, but also for a good reason, to unset it - if there's a leading whitespace ( line starts with space ) it would be gone without IFS=– Sergiy Kolodyazhnyy
Dec 5 at 0:07
@GeorgeUdosen Ah, yes, I found the issue - it's because of
IFS=. It unsets the variable temporarily, which is what is used for word splitting. IFS defaults to whitespace,tab,and newline. And it's a habit, but also for a good reason, to unset it - if there's a leading whitespace ( line starts with space ) it would be gone without IFS=– Sergiy Kolodyazhnyy
Dec 5 at 0:07
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