Sep 14, 2012 · In Bash, there appear to be several variables which hold special, consistently-meaning values. For instance, ./myprogram &; echo $! will return the PID of the process which backgrounded myprog...

It depends on the Test Construct around the operator. Your options are double parentheses, double brackets, single brackets, or test. If you use ((…)), you are testing arithmetic equality with == as in C: $ (( 1==1 )); echo $? 0 $ (( 1==2 )); echo $? 1 (Note: 0 means true in the Unix sense and a failed test results in a non-zero number.) Using -eq inside of double parentheses is a …

What are primaries? I call them "switches", but the bash documentation that you linked to refers to the same thing as "primaries" (probably because this is a common term used when discussing parts of a boolean expression). Background and docs In sh scripts if is a command that takes a command as its argument, executes it and tests its return code.

Oct 4, 2008 · Related discusions: bash for loop: a range of numbers and unix.stackexchange.com - In bash, is it possible to use an integer variable in the loop control of a for loop?

Modern shells such as Bash and Zsh have inherited this construct from Ksh, but it is not part of the POSIX specification. If you're in an environment where you have to be strictly POSIX compliant, stay away from it; otherwise, it's basically down to personal preference.

Feb 10, 2010 · How do I compare a variable to a string (and do something if they match)?

Apr 18, 2012 · 59 $ man bash -e file True if file exists. -f file True if file exists and is a regular file. A regular file is something that isn't a directory, symlink, socket, device, etc.

Is there any comprehensive list of characters that need to be escaped in Bash? Can it be checked just with sed? In particular, I was checking whether % needs to be escaped or not. I tried echo "h...

Jan 16, 2014 · You can find a very nice reference for bash's [ aka test builtin's operators here, or by running help test in a bash shell or info bash test or info bash '[' from any shell¹. If you are using a different shell, just search for the description of its [ or test builtin in its documentation of if it doesn't have such a builtin², in the man page of the standalone test utility³ and you will find ...

Dec 2, 2011 · I have two shell scripts, a.sh and b.sh. How can I call b.sh from within the shell script a.sh?