push

(C) Martin Väth martin@mvath.de This project is under the BSD license 2.0 (“3-clause BSD license”). SPDX-License-Identifier: BSD-3-Clause

A POSIX shell function to treat a variable like an array, quoting args.

For installation simply copy the content of bin/ somewhere into your path with the executable bit being set or execute make (and "make install" as root).

To check from within a POSIX shell script whether Push 2.0 (or newer) is installed, and sourcing it if it is, you can use something like:

if SOME_VARIABLE=`push.sh 2>/dev/null`
then	eval "$SOME_VARIABLE"
else	echo "push.sh not installed" >&2
fi

Remark: An obsoleted method was to use instead

	. push.sh

The latter works for older versions of push or if one installs manually, but unless an appropriate PATH before sourcing is set, it fails when push.sh is replaced by a wrapper script which happens with the provided Makefile. Moreover, if push.sh is not available it stops the script.

After this you have the shell function Push.

Usage: Push [-c] VARIABLE [arguments]

The arguments will be appended to VARIABLE in a quoted manner (with quotes rarely used - the exact form depends on the version of push.sh) so that an eval "$VARIABLE" obtains the collected arguments (see examples). With option -c, VARIABLE will be cleared before arguments are appended: The first call for VARIABLE must always be done with -c. The return value is zero if $VARIABLE contains at least one pushed argument.

Scripts using Push must not use variables of the form Push*_ (the reason is that POSIX does not provide a local name scope, and so Push uses internally global variables of such a form)

Example 1

Push -c foo 'data with special symbols like ()"\' "'another arg'"
Push foo further args
eval "printf '%s\\n' $foo"
# Be aware that not only $foo but the whole command is eval'ed!

will output

data with special symbols like ()"\
'another arg'
further
args

Example 2

Remove the last argument from the argument list in a script

Push -c args
while [ $# -gt 1 ]
do	Push args "$1"
	shift
done
eval "set -- a $args"; shift
# Note: "set -- $args" can break with some shells if args is empty

Example 3

Quote a command for "su" correctly

Push -c files "$@" && su -c "cat -- $files"

uses su to cat files passed as arguments with root permissions, even if the arguments contain problematic symbols like spaces, <, or quotes.

Example 4

Pretty-print a command without loosing exactness

set -- source~1 'source 2' "source '3'"
Push -c v cp -- "$@" \~dest
printf '%s\n' "$v"

will output a command which reliably can be pasted by the user into a POSIX shell but which nevertheless is reasonably human-readable. The exact form of output might be subject to change in different versions of Push. Currently the output would look like:

cp -- source~1 'source 2' 'source '\'3\' '~dest'

It is not recommended to rely on any particular form of the output: Instead, Push itself should be used if information is needed as in the subsequent example.

Example 5

Omitting arguments for Push can be useful

Push -c data
SomeFunction
Push data || echo 'nothing was pushed to $data in SomeFunction'

This has the advantage that you need not rely on the implementation details of how Push stores the data in the variable (which may depend on the version of Push).

AUTHORS

Martin Väth (Main part) xofyarg (fix in Makefile)