Is there any way to nest backticks?

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> Is there any way to nest backticks? What I mean is follows:
> localhost% echo "You have `expr `frm | wc -l` - 1` messages."

Get rid of csh

in ksh or sh, you might try:

echo "You have `expr \`frm | wc -l\` - 1` messages."

If you _must_ use csh, then put this into a script:

#!/bin/sh
echo "You have `expr \`frm | wc -l\` - 1` messages."

For ksh, there is a more readable syntax (to me, anyway)…

$ echo "You have $(expr $(frm | wc -l) -1) messages."

Dave

Is there any way to nest backticks?

There's also the $() notation, found in POSIX-compliant shells:

$ echo You have $(expr $(frm | wc -l) - 1) messages.

Neater, simpler, and washes whiter.

Simon

Is there any way to nest backticks?

> Are there any differences between $() and backticks, except from how easy
> they are to nest?

Backticks are available in all shells, i.e., sh, ksh, bash, csh, …, while $(…) can be found in ksh, bash, and other POSIX shells.

You're always on the safe side when you use backticks, however, this can be a pain in the neck when nesting.

Jens M. Felderhoff

Is there any way to nest backticks?

The backtick form does an extra level of quote processing before executing the contained command, and the $() form doesn't, so you can test a command outside of $() and not have to worry about adding quotes. Certain kinds of commands work poorly if at all inside backticks; the examples of this I've seen all involve here-documents. In addition, though it's not as big a deal, $(<filename) does the same thing as `cat filename` without creating another process.

Eric Amick

documented on: 1999.11.04 Thu 16:52:36