2012年4月3日 · What does a dollar sign followed by an at-sign (@) mean in a shell script? For example: umbrella_corp_options $@

$(command) is “command substitution”. As you seem to understand, it runs the command, captures its output, and inserts that into the command line that contains the $(…); e.g., $ ls -ld $(date +%B).txt -rwxr-xr-x 1 Noob Noob 867 Jul 2 11:09 July.txt ${parameter} is “parameter substitution”. A lot of information can be found in the shell’s man page, bash (1), under the “ …

I'm trying to learn shell scripting, and I need to understand someone else's code. What is the $? variable hold? I can't Google search the answer because they block punctuation characters.

2011年2月20日 · When going through one shell script, I saw the term "$?". What is the significance of this term?

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 …

2010年7月12日 · What is the purpose of a command that does nothing, being little more than a comment leader, but is actually a shell builtin in and of itself? It's slower than inserting a comment into your scripts...

What can you do with the eval command? Why is it useful? Is it some kind of a built-in function in bash? There is no man page for it..

2012年11月12日 · I am a system administrator and I have been asked to run a linux script to clean the system. The command is this: perl script.pl > output.log & so this command is ending with a & sign,...

2012年12月14日 · That is called a shebang, it tells the shell what program to interpret the script with, when executed. In your example, the script is to be interpreted and run by the bash shell. Some other example shebangs are: (From Wikipedia) #!/bin/sh — Execute the file using sh, the Bourne shell, or a compatible shell #!/bin/csh — Execute the file using csh, the C shell, or a compatible shell #!/usr ...

command-line - what is the purpose of &&? In shell, when you see $ command one && command two the intent is to execute the command that follows the && only if the first command is successful. This is idiomatic of Posix shells, and not only found in Bash. It intends to prevent the running of the second process if the first fails.