It is always worth while using the interactive interpreter first:-
This is a simple longhand starter that requires nothing but a bash terminal.
OSX 10.12.4, default bash terminal.
Code:
Last login: Thu Apr 27 10:53:04 on ttys000
AMIGA:amiga~> echo '2412
> 2413
> 2456
> 2134
> 2134
> 2244
> 2526' > /tmp/24.txt
AMIGA:amiga~> while read -r line; do if [ "${line:0:2}" == "24" ]; then echo "${line}"; fi; done < /tmp/24.txt
2412
2413
2456
AMIGA:amiga~> _
@wisecracker, when using the shell's read command rather than a line processing external utility to process all the characters on the line, it is best to use IFS= to prevent the interpretation of whitespace (otherwise it would also match lines starting with 24). Likewise when printing the result, it is best to use printf to avoid interpretation by the non-standard echo command, that you previously avoided with the -r option.
So:
Code:
while IFS= read -r line
do
....
printf "%s\n" "$line"
done < file
--
Note:
if
Code:
[ "${line:0:2}" == "24" ]
should syntactically be either
Code:
[ "${line:0:2}" = 24 ]
or
Code:
[[ ${line:0:2} == 24 ]]
since ${var:pos:num} is bash/ksh93/zsh, one might also use:
Code:
[[ $line == 24* ]]
Last edited by Scrutinizer; 04-27-2017 at 07:21 AM..
This prints 18th field where that field number - 18 - starts with a 24.
Your grep command does not match what you actually need, and neglected to mention the field requirement. It helps both you and the people helping you to give enough information to start with. The more you assume the less we can help you.
Code:
wc -l
counts lines it does not print field #18. If you want find how many lines match then pipe the output of the above awk into wc -l
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