[Discussion] POSIX, the Love of Backticks and All That Jazz Post: 302990548

Sponsored Content

Top Forums UNIX for Advanced & Expert Users [Discussion] POSIX, the Love of Backticks and All That Jazz Post 302990548 by wisecracker on Saturday 28th of January 2017 07:01:01 AM

01-28-2017

Registered User

Quote:

Originally Posted by Don Cragun

But, when writing new scripts (unless you intend to have them run on a pure Bourne shell that doesn't have $(command) command substitution), I would always suggest using the $(command) form... Note that:

$(command) command substitutions can be nested,
`command` command substitutions cannot be nested, and
if you need to quote the results of a command substitution where the command contains a double-quoted string, the double quotes inside a $(command) command substitution are not affected by double quotes outside the command substitution; but double quotes inside a `command` command substitution produce undefined results if the command substitution is inside double quotes.

I came across something like this in the early days of AudioScope and SOX.
I just assumed that it was me not coding correctly.
Thanks for the info.

wisecracker

View Public Profile for wisecracker

Find all posts by wisecracker

9 More Discussions You Might Find Interesting

1. Shell Programming and Scripting

Perl - backticks v system in if statements

Can someone explain the difference between backticks and system when evaluated in these if statements: sub getDate { print "start date\n"; if ( system("/bin/date") ) { print "can't get date\n"; exit(2); } print "finish date\n"; } Returns the following: start date Thu...

2. Shell Programming and Scripting

Backticks within backticks?

Hi, I'm trying to do something like this: range= `expr `date '+%m'` - 1` and it does not work. How can I tell it to evaluate an expression within another expression evaluation? I was at first worried that `date '+%m'` would return a string but apparently expr does the math okay normally, so the...

3. UNIX for Dummies Questions & Answers

sed: removing backticks from certain lines

Hi, I would like to change some lines in my mysql-dump, because there a syntax problems with some version of mysql. I 'd like to change USE �someDatabase�; to USE someDatabase; (without backticks) using the sed command in the shell Thanks & best regards Bernd

4. Shell Programming and Scripting

Am I abusing backticks?

I'm always concerned I might be abusing backticks within my scripts. A current script I'm writing has this for example: stripscriptname=`echo $scriptname | sed 's/$.*$\..*/\1/'` stripsearch=`echo $searchpattern | tr -d ' ,/'` Both of these variables are set inside the script (in fact,...

5. Shell Programming and Scripting

Difference between using xargs and backticks

Hey all. Just a fast question, what is the technical difference between using back ticks and using xargs to perform a command? Here's an example Find /mydir -name *.conf |xargs rm Vs Rm 'find /mydir -name *.conf' Is there a performance hit? I know they do the same thing but which is...

6. Red Hat

perl backticks: can't redirect output.

Hi everyone. This is a bit of a perl/linux mixed question. I am trying to redirect STDOUT of chsh by using the following line of perl code. system ("chsh -s /sbin/nologin $testing 1>/dev/null"); This should redirect STDOUT to /dev/null but it won't do that for some odd reason. Any ideas or...

7. Shell Programming and Scripting

Help with remove backticks in a text file

Input file: 'data_1' 'data_10' 'data1311' '235data_13' Desired output: data_1 data_10 data1311 235data_13 Can I know how to remove back tick"'" in a file? Many thanks for advice.

8. Shell Programming and Scripting

SSH and Backticks [solved]

I have been testing a new script and cannot figure out why my `cat spath` will not execute on the remote machine? sudo ssh -p 22344 -o "PasswordAuthentication no" -o "HostbasedAuthentication yes" -l testuser 192.168.1.6 "find `cat spath` -depth" cat: spath: No such file or directory but...

9. Shell Programming and Scripting

Nesting backticks

I'm trying to make a dialog window that prints the output of grep that takes the output of find. Unfortunately my nested backticks don't work. Here is the dialog window: dialog --stdout --title "test" --backtitle "test" --msgbox "Test:\n `grep -l "${tablica}" `find $string``" 16 60I think I...

LEARN ABOUT FREEBSD

mac_free

MAC_FREE(3)						   BSD Library Functions Manual 					       MAC_FREE(3)

NAME

     mac_free -- free MAC label

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/mac.h>

     int
     mac_free(mac_t label);

DESCRIPTION

     The mac_free() function frees the storage allocated to contain a mac_t.

RETURN VALUES

     The mac_free() function always returns 0.	WARNING: see the notes in the BUGS section regarding the use of this function.

SEE ALSO

     mac(3), mac_get(3), mac_prepare(3), mac_set(3), mac_text(3), posix1e(3), mac(4), mac(9)

STANDARDS

     POSIX.1e is described in IEEE POSIX.1e draft 17.  Discussion of the draft continues on the cross-platform POSIX.1e implementation mailing
     list.  To join this list, see the FreeBSD POSIX.1e implementation page for more information.

HISTORY

     Support for Mandatory Access Control was introduced in FreeBSD 5.0 as part of the TrustedBSD Project.

BUGS

     POSIX.1e specifies that mac_free() will be used to free text strings created using mac_to_text(3).  Because mac_t is a complex structure in
     the TrustedBSD implementation, mac_free() is specific to mac_3, and must not be used to free the character strings returned from
     mac_to_text().  Doing so may result in undefined behavior.

BSD
								 December 21, 2001							       BSD