Security implications of forgetting to quote a variable in bash/POSIX shellsIf you’ve been following unix.stackexchange.com for a while, youshould hopefully know by now that leaving a variableunquoted in list context (as in echo $var) in Bourne/POSIXshells (zsh being theUnix & Linux Stack ExchangeStéphane Chazelas [https://unix.

You might ever get confused because some bash config scripts are not executed, but they are sometimes executed multiple times. This post will reveal the reason for these phenomena. The basic definitions When being invoked with none of these options: --noprofile, --norc, --rcfile, --init-file, a bash session defines the startup

Some collected miscellaneous in bash * Shell expansions order [https://www.gnu.org/software/bash/manual/html_node/Shell-Expansions.html#Shell-Expansions] : Brace Expansion, Tilde Expansion, Shell Parameter Expansion, Command Substitution, Arithmetic Expansion, Process Substitution, Word Splitting, Filename Expansion, Quote Removal. * List operators precedence [https://www.gnu.org/software/bash/manual/html_

Intuitively, there are 3 concepts in file descriptor in bash: file descriptor number, file descriptor, and the file. File descriptor numbers are 0, 1, 2, ..., which usually refers to a file descriptor or nothing. A file descriptor is an object issued by operating system to access a file. A file

This post summarizes all types of pipelines, redirections in bash. -------------------------------------------------------------------------------- Basic * Continuous pipeline [https://www.gnu.org/software/bash/manual/html_node/Pipelines.html#Pipelines] command1 | command2: standard output of command1 is redirected as standard input of command2. Standard error of the command1 is redirected to /dev/stderr as

In bash, empty value and not defined value are different. This post will show how to recognize them correctly. Use Conditional Expressions Conditional Expressions official reference [https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html#Bash-Conditional-Expressions] * [[ $var ]] returns true if and only if var has non-zero length. * [[ -z

As long as there is a relative path in the PATH environment variable, find -execdir is totally unsafe and highly unrecommended. Assume that your PATH value is .:/usr/bin:/sbin:/bin:/snap/bin, in the directory which contains the file founded via find -execdir command, there is an executable file

The Grymoire’s tutorial on AWKThe Grymoire - Tutorial on the AWK program language. [http://www.grymoire.com/Unix/Awk.html]Samples * awk -f awk-script.awk input-file.txt * awk 'BEGIN {print "hello"} {print $0} END {print "end"}' input-file.txt * cat input-file.txt | awk -f awk-script.awk * awk -v awk_

Based on this StackExchange question [https://unix.stackexchange.com/questions/418429/find-intersection-of-lines-in-two-files] . I did a benchmark on intersection methods. There are two files that contain uniquely sorted lines. Our task is to find the number of lines that are exactly the same in both these files. Benchmark environment $ lsb_release

I got a situation of finding the maximal number of occurrences of characters in a line of a file. Based on this SO answer [https://stackoverflow.com/a/16679640/1398479]. I summarized all methods: * variable expansion: cnt="${line//[^:]}"; echo "${#cnt}" * tr: cnt="$(tr -dc : <<<"${line}")"; echo "${#cnt}" * awk: awk -F: