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
Old 01-27-2017
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:
Mod Comment 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.
 

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... (5 Replies)
Discussion started by: gjkeenan
5 Replies

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 Replies)
Discussion started by: jeriryan87
3 Replies

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 (5 Replies)
Discussion started by: bjb
5 Replies

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,... (2 Replies)
Discussion started by: mglenney
2 Replies

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... (1 Reply)
Discussion started by: msarro
1 Replies

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... (6 Replies)
Discussion started by: austinharris43
6 Replies

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. (3 Replies)
Discussion started by: perl_beginner
3 Replies

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... (0 Replies)
Discussion started by: metallica1973
0 Replies

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... (2 Replies)
Discussion started by: Starting_Leaf
2 Replies
TAIL(1) 						    BSD General Commands Manual 						   TAIL(1)

NAME
tail -- display the last part of a file SYNOPSIS
tail [-f | -F | -r] [-b number | -c number | -n number] [file ...] DESCRIPTION
The tail utility displays the contents of file or, by default, its standard input, to the standard output. The display begins at a byte, line or 512-byte block location in the input. Numbers having a leading plus (``+'') sign are relative to the beginning of the input, for example, ``-c +2'' starts the display at the second byte of the input. Numbers having a leading minus (``-'') sign or no explicit sign are relative to the end of the input, for example, ``-n 2'' displays the last two lines of the input. The default starting location is ``-n 10'', or the last 10 lines of the input. The options are as follows: -b number The location is number 512-byte blocks. -c number The location is number bytes. -f The -f option causes tail to not stop when end of file is reached, but rather to wait for additional data to be appended to the input. The -f option is ignored if the standard input is a pipe, but not if it is a FIFO. -F The -F option is the same as the -f option, except that every five seconds tail will check to see if the file named on the command line has been shortened or moved (it is considered moved if the inode or device number changes) and, if so, it will close the current file, open the filename given, print out the entire contents, and continue to wait for more data to be appended. This option is used to follow log files though rotation by newsyslog(8) or similar programs. -n number The location is number lines. -r The -r option causes the input to be displayed in reverse order, by line. Additionally, this option changes the meaning of the -b, -c and -n options. When the -r option is specified, these options specify the number of bytes, lines or 512-byte blocks to display, instead of the bytes, lines or blocks from the beginning or end of the input from which to begin the display. The default for the -r option is to display all of the input. If more than a single file is specified, each file is preceded by a header consisting of the string ``==> XXX <=='' where ``XXX'' is the name of the file. The tail utility exits 0 on success, and >0 if an error occurs. SEE ALSO
cat(1), head(1), sed(1) STANDARDS
The tail utility is expected to be a superset of the IEEE Std 1003.2-1992 (``POSIX.2'') specification. In particular, the -b, -r and -F options are extensions to that standard. The historic command line syntax of tail is supported by this implementation. The only difference between this implementation and historic versions of tail, once the command line syntax translation has been done, is that the -b, -c and -n options modify the -r option, i.e. ``-r -c 4'' displays the last 4 characters of the last line of the input, while the historic tail (using the historic syntax ``-4cr'') would ignore the -c option and display the last 4 lines of the input. HISTORY
A tail command appeared in Version 7 AT&T UNIX. BUGS
When using the -F option, tail will not detect a file truncation if, between the truncation and the next check of the file size, data written to the file make it larger than the last known file size. BSD
June 6, 1993 BSD
All times are GMT -4. The time now is 11:38 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy