Linux study notes: Understanding SHELL

Alias displays all current command aliases aliaslm & quot; ls-al & quot; command alias unaliaslm cancel command alias type similar to whichexprot setting or display environment variable exprot alias show all current command alias lm = "ls-al" command alias unalias lm cancel command alias type similar to whichexprot set or display the environment variable exprot PATH = "$ PATH ": /sbin add/sbin in PATH echo $ PATH display PATH bash enter subroutine name = yang set variable unset name cancel variable echo $ name display variable content myname = "$ name its me "& myname = '$ name its Me' $ variable content missing $ name in single quotes ciw =/etc/sysconfig/network-scripts/set path env to list all environment variables Echo $ RANDOM: Display the randomly generated number set. set SHELLPS1 = '[u @ h w A ##] $'. set the prompt character. [root @ linux ~] # Read [-pt] variable ----------- read the variable parameter input by the keyboard:-p: the rear can receive a prompt character! -T: The number of seconds that the backend can wait !』 Declare declares the shell variable ulimit-a to display all restrictions. ls/tmp/yang & echo "exist" | echo "not exist" means, after ls/tmp/yang is executed, if it is correct, execute echo "exist". if there is a problem, execute echo "not exist" echo $ PATH | cut-D ': '-f 5 uses the separator, read 5th-segment content export | cut-c 10-20 read 10th-20 bytes of content last | grep 'root' search for a row with root, add [-v] to reverse search cat/etc/passwd | sort display cat/etc/passwd | wc display "line, word count, number of bytes 』 Regular representation[Root @ test root] # grep [-acinv] 'search for the string' filename Parameter description:-A: Search for binary files using text files.-c: count the number of times that the 'searchstring' is found.-I: The Case sensitivity is ignored. Therefore, the case sensitivity is the same.-n: by the way, the output line number-v is selected in reverse direction, that is, the line without the 'searchstring' content is displayed! Grep-n '123.txt search the character search the specific string grep-n' t [ea] st'123.txt search test or taste use [] to search for the set character grep-n '[^ g] oo' 123.txt select [^] grep-n '[0-9] '123.txt search for numbers with 0-9 grep-n' ^ the '123.txt search start with the row and start with the search ^ grep-n' ^ [^ a-zA-Z] '123.txt search does not start with a letter grep-n '[ a-z] $ '123.txt search for the end of a-z line search $ grep-n' g .. d' 123.txt: search for any character starting with "g" and ending with "d. grep-n 'Ooo * '123.txt search contains at least two oo repeated characters * sed text stream editor uses script commands to process text files awd mode scanning and processing language nl 123.txt | sed' 2, 5d 'delete content from the second to fifth rows diff compare file difference cmp compare two files difference patch file pr to print file formatting