Linux commands

OS Version

uname -srm
cat /proc/version
hostnamectl

Make archive

tar cvf - /etc /home | gzip > test.tar.gz

Extract archive

gunzip < test.tar.gz | tar xvf -

Convert file's encoding

iconv -f UTF-8 -t CP1252 <in_file> > <out_file>

Linux Performance Monitoring

vmstat
iostat

Information about the Linux networking

netstat -a -n

Monitor processes

top

Use [] in grep to find a process and not include the grep command itself when you pipe ps -ef output to grep

ps -ef | grep inet[d]

Use the IFS shell variable to split a line into fields:

grep root /etc/passwd | IFS=: read user x1 uid gid x2 home shell
print $uid $home

To send all output (stdout and stderr) generated by a command to the same file use

command >file 2>&1

To send all output (stdout and stderr) generated by a command to a file and to the terminal (stdout) use

command 2>&1 | tee file

String Substitution Operators

${varname:-value} Return value of varname if it exists and it is not null; otherwise return value.

${varname:=value} Return value of varname if it exists and it is not null; otherwise set varname to value and return value.

${varname:?message} Return value of varname if it exists and it is not null; otherwise print varname: message and abort current command or script. Default message is parameter null or not set.

${varname:+value} Return value, if varname exists and it is not null; otherwise return null.

Pattern-matching Operators

${varname#pattern} If pattern matches the beginning of varname's value, delete the shortest part that matches and return the rest.

${varname##pattern} If pattern matches the beginning of varname's value, delete the longest part that matches and return the rest.

${varname%pattern} If pattern matches the end of varname's value, delete the shortest part that matches and return the rest.

${varname%%pattern} If pattern matches the end of varname's value, delete the longest part that matches and return the rest.

expr command

expr index string string2 to display the numerical position in string of first character in string2 that matches.

expr substr string position length extracts length characters of substring from string starting at position.