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https://github.com/vaeth/push

A POSIX shell function to treat a variable like an array, quoting args.
https://github.com/vaeth/push

posix quotes quoting-args shell

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

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README 

        
# push



(C) Martin Väth 

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)