What does if [ "${1}" == "pre" ]; do?


Login or Register to Reply

 
Thread Tools Search this Thread
# 1  
What does if [ "${1}" == "pre" ]; do?

I am trying to run a command after my computer returns from suspend.

Script came from here.

Running scripts before and after suspend with systemd << Just another Linux geek

(It is not currently not working.)

What does the if do?

Code:
#!/bin/sh
#
# Created 3/31/19 in /usr/lib/systemd/system-sleep/
if [ "${1}" == "pre" ]; then
  # Do the thing you want before suspend here, e.g.:
  echo "we are suspending at $(date)..." > /tmp/systemd_suspend_test
elif [ "${1}" == "post" ]; then
  # Do the thing you want after resume here, e.g.:
  echo "...and we are back from $(date)" >> /tmp/systemd_suspend_test
  gxmessage -fg red -font  'sans 30' -timeout 3  ' Computer has now resumed from suspend state.'
fi


Last edited by drew77; 04-01-2019 at 11:56 AM..
# 2  
Quote:
Originally Posted by drew77
Code:
if [ "${1}" == "pre" ]; then

"${1}" is the long form of "$1". It is the first positional parameter the script got. If you call a script like this:

Code:
$ ./somescript.sh first second third

then inside ./somescript.sh the variable "$1" would be set to "first", the variable "$2" would be set to "second" and "$3" would be set to "third". So this line is asking if the first parameter to the script equals "pre".

I hope this helps.

bakunin
# 3  
Also note that syntactically
Code:
if [ "${1}" == "pre" ]; then

should be:
Code:
if [ "${1}" = "pre" ]; then

Whatever happens to be the shell /bin/sh on your system may or may not be able to handle this correctly..

Another thing to verify is that gxmessage needs to be installed and in your default search path in order for the script to work, since the PATH variable is not set inside that script.
This User Gave Thanks to Scrutinizer For This Post:
# 4  
Thanks.

All my scripts are in /home/andy/bin.

Code:
echo $PATH
/home/andy/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin


Last edited by drew77; 04-01-2019 at 11:50 AM..
# 5  
man systemd-suspend.service

The documentation leaves much to be desired.

Code:
SYSTEMD-SUSPEND.SERVICE(8)                                        systemd-suspend.service                                       SYSTEMD-SUSPEND.SERVICE(8)

NAME
       systemd-suspend.service, systemd-hibernate.service, systemd-hybrid-sleep.service, systemd-suspend-then-hibernate.service, systemd-sleep - System
       sleep state logic

SYNOPSIS
       systemd-suspend.service

       systemd-hibernate.service

       systemd-hybrid-sleep.service

       systemd-suspend-then-hibernate.service

       /lib/systemd/system-sleep

DESCRIPTION
       systemd-suspend.service is a system service that is pulled in by suspend.target and is responsible for the actual system suspend. Similarly,
       systemd-hibernate.service is pulled in by hibernate.target to execute the actual hibernation. Finally, systemd-hybrid-sleep.service is pulled in by
       hybrid-sleep.target to execute hybrid hibernation with system suspend and pulled in by suspend-then-hibernate.target to execute system suspend with
       a timeout that will activate hibernate later.

       Immediately before entering system suspend and/or hibernation systemd-suspend.service (and the other mentioned units, respectively) will run all
       executables in /lib/systemd/system-sleep/ and pass two arguments to them. The first argument will be "pre", the second either "suspend",
       "hibernate", "hybrid-sleep", or "suspend-then-hibernate" depending on the chosen action. Immediately after leaving system suspend and/or
       hibernation the same executables are run, but the first argument is now "post". All executables in this directory are executed in parallel, and
       execution of the action is not continued until all executables have finished.

       Note that scripts or binaries dropped in /lib/systemd/system-sleep/ are intended for local use only and should be considered hacks. If applications
       want to react to system suspend/hibernation and resume, they should rather use the Inhibitor interface[1].

       Note that systemd-suspend.service, systemd-hibernate.service, and systemd-hybrid-sleep.service systemd-suspend-then-hibernate.service should never
       be executed directly. Instead, trigger system sleep states with a command such as "systemctl suspend" or similar.

       Internally, this service will echo a string like "mem" into /sys/power/state, to trigger the actual system suspend. What exactly is written where
       can be configured in the "[Sleep]" section of /etc/systemd/sleep.conf or a sleep.conf.d file. See systemd-sleep.conf(5).

OPTIONS
       systemd-sleep understands the following commands:

       -h, --help
           Print a short help text and exit.

       --version
           Print a short version string and exit.

       suspend, hibernate, hybrid-sleep, suspend-then-hibernate
           Suspend, hibernate, suspend then hibernate, or put the system to hybrid sleep.

SEE ALSO
       systemd-sleep.conf(5), systemd(1), systemctl(1), systemd.special(7), systemd-halt.service(8)

NOTES
        1. Inhibitor interface
           https://www.freedesktop.org/wiki/Software/systemd/inhibit

systemd 237                                                                                                                     SYSTEMD-SUSPEND.SERVICE(8)

Login or Register to Reply

|
Thread Tools Search this Thread
Search this Thread:
Advanced Search

More UNIX and Linux Forum Topics You Might Find Helpful
Bash script - Print an ascii file using specific font "Latin Modern Mono 12" "regular" "9"
jcdole
Hello. System : opensuse leap 42.3 I have a bash script that build a text file. I would like the last command doing : print_cmd -o page-left=43 -o page-right=22 -o page-top=28 -o page-bottom=43 -o font=LatinModernMono12:regular:9 some_file.txt where : print_cmd ::= some printing...... Shell Programming and Scripting
1
Shell Programming and Scripting
Using "mailx" command to read "to" and "cc" email addreses from input file
asjaiswal
How to use "mailx" command to do e-mail reading the input file containing email address, where column 1 has name and column 2 containing “To” e-mail address and column 3 contains “cc” e-mail address to include with same email. Sample input file, email.txt Below is an sample code where...... UNIX for Dummies Questions & Answers
2
UNIX for Dummies Questions & Answers
awk command to replace ";" with "|" and ""|" at diferent places in line of file
shis100
Hi, I have line in input file as below: 3G_CENTRAL;INDONESIA_(M)_TELKOMSEL;SPECIAL_WORLD_GRP_7_FA_2_TELKOMSEL My expected output for line in the file must be : "1-Radon1-cMOC_deg"|"LDIndex"|"3G_CENTRAL|INDONESIA_(M)_TELKOMSEL"|LAST|"SPECIAL_WORLD_GRP_7_FA_2_TELKOMSEL" Can someone...... Shell Programming and Scripting
7
Shell Programming and Scripting
Explain the line "mn_code=`env|grep "..mn"|awk -F"=" '{print $2}'`"
Lokesha
Hi Friends, Can any of you explain me about the below line of code? mn_code=`env|grep "..mn"|awk -F"=" '{print $2}'` Im not able to understand, what exactly it is doing :confused: Any help would be useful for me. Lokesha... UNIX for Dummies Questions & Answers
4
UNIX for Dummies Questions & Answers

Featured Tech Videos