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Give a default/non-null value in order to avoid the "unary operator expected" error

Posted 02-19-2014 at 03:00 PM by the dsc (linux-related notes)

Tags bash

Quote:

Originally Posted by cfajohnson

Quote:

i am trying to compare a value with value 50. but i am getting
"[: -lt: unary operator expected"

I am using

if [ $j -lt 50 ]
then
echo "------------"

fi

Make sure that $j expands to a value. Best is to set it explicitly, but you can also give it a default value (0 in this example):

Code:
if [ ${j:-0} -lt 50 ]

http://www.unix.com/302295072-post3.html...

the dsc

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Bash Scripting for Dummies and Geniuses

Posted 11-20-2013 at 09:18 AM by rtmistler
Updated 05-25-2020 at 08:43 AM by rtmistler

Tags bash, command line, programming, scripting

One only need look at LinuxQuestions.org to notice the great amount of script (and code) questions and varieties of comments to realize that we all have varying opinions about bash programming.

Many questions are very complicated, as are the resulting answers and script recommendations. I've noticed that two fundamental points are invariably overlooked by the questioners, and many of the comments:

Quote:

"All programming is the use of simple operations to solve complex

...

rtmistler

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Run C/C++ Code As Script

Posted 09-04-2013 at 11:36 AM by rainbowsally
Updated 08-06-2014 at 07:13 AM by rainbowsally (new version)

Tags bash, computer mad science, simple c

runc update Sept 27, 2013

http://rainbowsally.org/rainbowsally...-rs-1.2.tar.gz

Changes slist_count() to standard objlist syntax and removes slist_getCount()
Removes destructor functions from objlist so that each class explicitly free anything memory they allocate.
Added atexit() function to tmpmem/tmpstr functions.
Most of these changes address memory leaks and/or memory that remains accessible after the apps close.

--------------...

rainbowsally

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bash read file

Posted 05-24-2013 at 09:20 AM by NullTerminator
Updated 05-24-2013 at 11:26 AM by NullTerminator

Tags bash, bash find, bash read, read

Sample of while loop to process input

Code:

#!/bin/sh
##################################
# Purpose: Cleanup any confirmation reports (*.pdf) older than xx days
# Called By:  batch daily cleanup process,  /Applications/xyz/distributor.sh
# Author: jeb
# Date: 4/20/07
# Comments: The while loop is preferred over the find -exec rm {} syntax because it
#           does not spawn a process for each file to be deleted.
#           The script expects

...

NullTerminator

LQ Newbie

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A good $PS1 for displaying long paths in the bash prompt

Posted 03-13-2013 at 11:29 PM by the dsc (linux-related notes)
Updated 03-13-2013 at 11:30 PM by the dsc

Tags bash, prompt, ps1

Code:

PS1='${debian_chroot:+($debian_chroot)}\t \u $(if [ ${#PWD} -gt 30 ] ; then myPWD="${PWD:0:12}…/\W" ; myPWD="${myPWD:0:25}…" ; else myPWD=$PWD; fi ; echo $myPWD) $ '

It will display full paths smaller than 30 characters entirely, but for longer paths it will get only the first characters of the whole path, and the fist characters of the last folder in the full path.

The end result is something like:

HH:MM:SS tuxguy /home/tuxguy/mystuf.../xmas...

the dsc

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