[Discussion] POSIX, the Love of Backticks and All That Jazz Post: 302990516

Sponsored Content

Top Forums UNIX for Advanced & Expert Users [Discussion] POSIX, the Love of Backticks and All That Jazz Post 302990516 by bakunin on Friday 27th of January 2017 12:17:49 PM

01-27-2017

Registered User

Quote:

Originally Posted by Peasant

If i'm not mistaken backquotes are still the lowest common denominator for command substitution if you wish your scripts to work anywhere without touching

This is an interesting argument.

IMHO the "gold standard" of portability is POSIX: if something is POSIX, then it can (and should) be used, if it not, it should be handled with extreme care (and eventually not be used in absence of compelling reasons why it should).

The construct $(..) now is in fact the POSIX-standard for doing this (subshells) and backticks `...` are deprecated. This is why i use the former rather than the latter and recommend this practice to others.

For the same reason i write i.e. tail -n 5 instead of tail -5. The former is POSIX, the latter deprecated. It may be that there is some (really old) system out there which would not recognise the new syntax but only the old one. This risk i am willing to take because, on the the other hand, there might be a really new system which has cut off old behaviorisms and only understands the current syntax.

I hope this helps.

bakunin

Moderator's Comments:

PS: this discussion is very interesting but we are getting off topic in relation the threads original theme. If anyone wants to continue this i suggest to split this thread and carry on in a new one. Just post here if you want to contribute and i will take care of the splitting if there are any takers.

bakunin

View Public Profile for bakunin

Find all posts by bakunin

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 HPUX

rc.config

rc.config(4)						     Kernel Interfaces Manual						      rc.config(4)

NAME

       rc.config, rc.config.d - files containing system configuration information

SYNOPSIS

DESCRIPTION

       The  system  configuration  used  at  startup  is  contained in files within the directory The file sources all of the files within and and
       exports their contents to the environment.

   /etc/rc.config
       The file is a script that sources all of the scripts, and also sources To read the  configuration  definitions,	only  this  file  need	be
       sourced.   This	file  is  sourced by whenever it is run, such as when the command is run to transition between run states.  Each file that
       exists in is sourced, without regard to which startup scripts are to be executed.

   /etc/rc.config.d
       The configuration information is structured as a directory of files, rather than as a single file containing the  same  information.   This
       allows  developers  to  create and manage their own configuration files here, without the complications of shared ownership and access of a
       common file.

   /etc/rc.config.d/* Files
       This is where files containing configuration variable assignments are located.

       Configuration scripts must be written to be read by the POSIX shell, and not the Bourne shell, or In some cases, these files must  also	be
       read  and  possibly modified by control scripts or the sam program.  See sd(4) and sam(1M).  For this reason, each variable definition must
       appear on a separate line, with the syntax:

       No trailing comments may appear on a variable definition line.  Comment statements must be on separate lines, with the comment character in
       column one.  This example shows the required syntax for configuration files:

       Configuration variables may be declared as array parameters when describing multiple instances of the variable configuration.  For example,
       a system may contain two network interfaces, each having a unique IP address and subnet mask (see ifconfig(1M)).  An example of such a dec-
       laration is as follows:

       Note  that  there  must	be  no requirements on the order of the files sourced.	This means configuration files must not refer to variables
       defined in other configuration files, since there is no guarantee that the variable being referenced is currently  defined.   There  is	no
       protection  against  environment variable namespace collision in these configuration files.  Programmers must take care to avoid such prob-
       lems.

   /etc/TIMEZONE
       The file contains the definition of the environment variable.  This file is required by POSIX.  It is sourced by at the same time the files
       are sourced.

SEE ALSO

       rc(1M).

																      rc.config(4)