The tabulator in bash

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Published on August 23rd 2010 - Listed in Linux Shell


I've just spent interesting 20mins with my boss, trying to figure out why Bash wouldn't recognize our command to not output lines containing tabulator entries.

The problem:

grep -v "\t" tempfile # does not work

Still shows lines with tab-entries. At first we thought maybe Bash has a problem recognizing the tabulator, so my idea was to use sed instead of grep:

sed -e '/\t/d' tempfile # works

It works with sed! So the \t is correctly recognized. Maybe a problem of grep only? After doing several tests, we finally found the solution. First we used an echo to force a tab sign within the grep command:

grep -v "$(echo -ne "\t")" tempfile # works

So as soon as a sub-shell is opened to 'translate' \t into a tab-sign it works, how it is also written in the bash-manpage:

Words of the form $'string' are treated specially.  The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows:
...
\t     horizontal tab
...

Which leads to the following and final solution:

grep -v $'\t' /tmp/tempfile # works


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