Shell – Store specific output to a shell variable

command-substitutionshelltext processingvariable

I am looking to store the output of the svn info command, more precisely the revision number into a variable for further processing. I just need the 4 stored.

$ svn info
[...]
Revision: 4
[...]

Best Answer

Using awk

awk works well for this:

rev=$(svn info | awk '/Revision:/{print $2}')

The code above uses command substitution, $(...), to capture the output of a command and assign it to a variable.

In the code above, awk reads the output of svn info and waits for a line that contains the string Revision:. When that line is found, it prints the second field on that line, which is be the revision number.

Using sed

It is also possible to do this using sed:

rev=$(svn info | sed -n '/Revision:/ s/.* //p')

With the -n option, sed will only print when we explicitly ask it to. /Revision:/ selects lines that contain the string Revision:. For those lines, a substitution command is performed that removes all characters up to the last blank on the line and then, due to the p option, the line is printed.

Using shell

while read -r name value
do 
    [ "$name" = Revision: ] && var="$value"
done < <(svn info)

The above uses redirection from process substition, < <(...), to supply the output of svn info to a while loop. For each iteration of the loop, the first word on the line is assigned to name and the rest of the line is assigned to value. If name is Revision:, then the shell variable var is assigned to value, which is the revision number.

Many, but not all, shells support process substitution. When, as above, redirection is combined with process substitution, the space between the two < is essential.

Related Solutions

How to Store Shell Script Output to a Variable

As explained in your question's comments, the variable RELEASE_COMMAND_OUTPUT will only get the STDOUT(standard output) of your command but not the STDERR (standard error), as it seems to be your case.

When in doubt about the output of your command you can use process substitution to mark the STDERR in red as in the following example:

command 2> >(while read line; do echo -e "\e[01;31m$line\e[0m" >&2; done)

Which is redirecting (the 2> part) the STDERR of the command as input to the while block which will print it in red in the terminal.

You can also do the opposite, marking the STDOUT as red with:

command | grep .

Because grep act only in STDOUT

NOTE: in some systems you may need to enable the color in grep using the flag --color=auto. On Macos and Linux usually it's enable by default.

Shell – How to store a string literal to a variable with no substitution or interpretation

If using GNU mv, you should rather do:

find . -type f -exec mv -t . {} +

With other mvs:

find . -type f -exec sh -c 'exec mv "$@" .' sh {} +

You should never embed {} in the sh code. That's a command injection vulnerability as the names of the files are interpreted as shell code (try with a file called `reboot` for instance).

Good point for quoting the command substitution, but because you used the archaic form (`...` as opposed to $(...)), you'd need to escape the inner double quotes or it won't work in sh implementations based on the Bourne shell or AT&T ksh (where "`basename "foo bar"`" would actually be treated as "`basename " (with an unmatched ` which is accepted in those shells) concatenated with foo and then bar"`").

Also, when you do:

mv foo/bar bar

If bar actually existed and was a directory, that would actually be a mv foo/bar bar/bar. mv -t . foo/bar or mv foo/bar . don't have that issue.

Now, to store those several arguments (-exec, sh, -c, exec mv "$@" ., sh, {}, +) into a variable, you'd need an array variable. Shells supporting arrays are (t)csh, ksh, bash, zsh, rc, es, yash, fish.

And to be able to use that variable as just $FLATTEN (as opposed to "${FLATTEN[@]}" in ksh/bash/yash or $FLATTEN:q in (t)csh), you'd need a shell with a sane array implementation: rc, es or fish. Also zsh here as it happens none of those arguments is empty.

In rc/es/zsh:

FLATTEN=(-exec sh -c 'exec mv "$@" .' sh '{}' +)

In fish:

set FLATTEN -exec sh -c 'exec mv "$@" .' sh '{}' +

Then you can use:

find . -type f $FLATTEN