I've been following the guidance here: Extract Substring Using RegExp in Plain Bash
I can't seem to get my code to work properly:
This echoes correctly:
for filename in ./unsent_xmls/*.xml; do
echo $filename | perl -lne 'print $& if /(\d{4})(?=-)/'
done
but when I try this it prints an empty result:
for filename in ./unsent_xmls/*.xml; do
package=$filename | perl -lne 'print $& if /(\d{4})(?=-)/'
echo $package
done
I've tried a number of different iterations.
There are two problems.
package=$filename produces no output to be piped to perlpackage is only set in the subshell that runs the left-hand side of the pipeline; it's not set after the pipeline completes.If all you want are the 4 digits preceding the first - in the file name, use
for filename in ./unset_xmls/*.xml; do
[[ $filename =~ ([[:digit:]]{4})- ]] && package=${BASH_REMATCH[1]}
echo "$package"
done
Three things: you still need the echo in the pipeline, you need $( ) to capture the output from the pipeline so you can assign it to a variable, and you should use double-quotes around variable references (to prevent possible parsing oddities):
for filename in ./unsent_xmls/*.xml; do
package=$(echo "$filename" | perl -lne 'print $& if /(\d{4})(?=-)/')
echo "$package"
done
perlcommand supposed to do? There's almost certainly a simpler way to do this inbashalone.perlalone :). But that perl matches the RE. If it matches, it prints "The string matched by the last successful pattern match". (Which is what$&means)