Difference between revisions of "Bash notes"

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set +o history
 
set +o history
 
</pre>
 
</pre>
 +
 +
== rename a group of files by extension ==
 +
 +
This is somewhat more clear
 +
<pre>
 +
for filename in *.jpg ; mv $filename `basename $filename .jpg`_2.jpg; done
 +
</pre>
 +
 +
This is more "correct" and doesn't require `basename`:
 +
 +
<pre>
 +
for filename in *.jpg ; mv $filename `basename $filename .jpg`_2.jpg; done
 +
</pre>
 +
  
 
== Variable Expansion and Substitution ==
 
== Variable Expansion and Substitution ==

Revision as of 13:58, 20 February 2008


Turn off bash history for a session

set +o history

rename a group of files by extension

This is somewhat more clear

for filename in *.jpg ; mv $filename `basename $filename .jpg`_2.jpg; done

This is more "correct" and doesn't require `basename`:

for filename in *.jpg ; mv $filename `basename $filename .jpg`_2.jpg; done


Variable Expansion and Substitution

Bash can do some freaky things with variables. It can do lots of other substitutions. See "Parameter Expansion" in the Bash man page.

  • ${foo#pattern} - deletes the shortest possible match from the left
  • ${foo##pattern} - deletes the longest possible match from the left
  • ${foo%pattern} - deletes the shortest possible match from the right
  • ${foo%%pattern} - deletes the longest possible match from the right
  • ${foo=text} - If $foo exists and is not null then return $foo. If $foo doesn't exist then create it and set value to text.

Statements

Loop on filenames in a directory

for foo in *; do {
  echo ${foo}
}; done

Loop on lines in a file

for foo in $(cat data_file.txt); do {
  echo ${foo}
}; done