How can you limit the count of standard output characters that is redirected to file?
asked Mar 29, 2011 at 21:58
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3 Answers
Other ways (external)
echo $out| head -c 20
echo $out | awk '{print substr($0,1,20) }'
echo $out | ruby -e 'print $_[0,19]'
echo $out | sed -r 's/(^.{20})(.*)/\1/'
Comments
You could use Command Substitution to wrap the output pre-redirection, then use the offset Parameter Expansion to limit the number of characters like so:
#!/bin/bash
limit=20
out=$(echo "this line has more than twenty characters in it")
echo ${out::limit} > /path/to/file
Proof of Concept
$ limit=20
$ out=$(echo "this line has more than twenty characters in it").
$ echo ${out::limit}
this line has more t
2 Comments
sarnold
Cripes, I never cease to be amazed at how much I don't know about bash.
SiegeX
@sarnold Parameter Expansion seems to be the biggest undervalued/unknown feature of not just
bash but any POSIX compliant shell. Time after time I see people calling basename or dirname which both can be done in native shell syntax using Parameter Expansion. See HERE for a good link on usage as well as a great site on bash.You can't do so directly into a file, but you can pipe through sed or head, etc. to pass on only part of the output. Or as @SiegeX says, capture the output in the shell (but I would be wary of that if the output mis likely to be large).
answered Mar 29, 2011 at 22:05
