Using variables in if statements If you want to do something when they don’t match, replace = with !=. You can read more about string operations and arithmetic operations in their respective documentation. Why do we use quotes around $x? You want the quotes around $x, because if it is empty, your Bash script encounters … Read more
The following reads a file passed as an argument line by line: This is the standard form for reading lines from a file in a loop. Explanation: IFS= (or IFS=”) prevents leading/trailing whitespace from being trimmed. -r prevents backslash escapes from being interpreted. Or you can put it in a bash file helper script, example … Read more
chmod u+x program_name. Then execute it. If that does not work, copy the program from the USB device to a native volume on the system. Then chmod u+x program_name on the local copy and execute that. Unix and Unix-like systems generally will not execute a program unless it is marked with permission to execute. The … Read more
You should use #!/usr/bin/env bash for portability: different *nixes put bash in different places, and using /usr/bin/env is a workaround to run the first bash found on the PATH. And sh is not bash.
Use cut: More generic:
[[ has fewer surprises and is generally safer to use. But it is not portable – POSIX doesn’t specify what it does and only some shells support it (beside bash, I heard ksh supports it too). For example, you can do to test whether a file exists. But with [, you have to quote $b, … Read more
File descriptor 1 is the standard output (stdout).File descriptor 2 is the standard error (stderr). Here is one way to remember this construct (although it is not entirely accurate): at first, 2>1 may look like a good way to redirect stderr to stdout. However, it will actually be interpreted as “redirect stderr to a file … Read more
Depending on what you want the file to contain: touch /path/to/file for an empty file somecommand > /path/to/file for a file containing the output of some command. eg: grep –help > randomtext.txt echo “This is some text” > randomtext.txt nano /path/to/file or vi /path/to/file (or any other editor emacs,gedit etc)It either opens the existing one for editing or creates & opens … Read more
The test command ([ here) has a “not” logical operator which is the exclamation point (similar to many other languages). Try this:
Note that the characters in $IFS are treated individually as separators so that in this case fields may be separated by either a comma or a space rather than the sequence of the two characters. Interestingly though, empty fields aren’t created when comma-space appears in the input because the space is treated specially. To access … Read more