2012年4月3日 · The shell splits tokens based on the contents of the IFS environment variable. Its default value is \t\n; i.e., whitespace, tab, and newline. Expanding "$@" gives you a pristine copy of the arguments passed. Expanding $@ may not.

2012年9月17日 · The return value is 0 if the string matches the pattern, and 1 otherwise. If the regular expression is syntactically incorrect, the conditional expression's return value is 2. If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters.

Try the following in the shell: ls somefile echo $? If somefile exists (regardless whether it is a file or directory), you will get the return value thrown by the ls command, which should be 0 (default "success" return value). If it doesn't exist, you should get a number other then 0. The exact number depends on the program.

The above (along with many more forms of ${parameter…something_else} constructs) are discussed at greater length in the shell’s man page, bash(1). A Note on Quotes. Note that you should always quote shell variables unless you have a good reason not to, and you’re sure you know what you’re doing. By contrast, while braces can be ...

2010年7月12日 · The first line, set -x, makes the shell print out the command before running it. It's quite a useful construct. The downside is that the usual echo Log message type of statement now prints the message twice. The colon method gets round that.

You can always check the man page of your shell. man bash says: Special Parameters # Expands to the number of positional parameters in decimal. Therefore a shell script can check how many parameters are given with code like this: if [ "$#" -eq 0 ]; then echo "you did not pass any parameter" fi

2019年8月1日 · The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. [...]? Expands to the exit status of the most recently executed foreground pipeline. ANSI C and POSIX then recommend that: 0 means the program was successful. other values: the program failed somehow.

I can't seem to be able to increase the variable value by 1. I have looked at tutorialspoint's Unix / Linux Shell Programming tutorial but it only shows how to add together two variables. I have tried the following methods but they don't work:

2021年10月27日 · 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.

What is the difference between =, == and -eq in shell scripting? Is there any difference between the following?