diff options
Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 36 |
1 files changed, 31 insertions, 5 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index 211d2944..a62bd167 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -11,6 +11,7 @@ contributors: - ["Rahil Momin", "https://github.com/iamrahil"] - ["Gregrory Kielian", "https://github.com/gskielian"] - ["Etan Reisner", "https://github.com/deryni"] + - ["Jonathan Wang", "https://github.com/Jonathansw" ] filename: LearnBash.sh --- @@ -54,6 +55,13 @@ echo '$Variable' # its name without $. If you want to use the variable's value, you should use $. # Note that ' (single quote) won't expand the variables! +# Parameter expansion ${ }: +echo ${Variable} +# This is a simple usage of parameter expansion +# Parameter Expansion gets a value from a variable. It "expands" or prints the value +# During the expansion time the value or parameter are able to be modified +# Below are other modifications that add onto this expansion + # String substitution in variables echo ${Variable/Some/A} # This will substitute the first occurrence of "Some" with "A" @@ -68,6 +76,12 @@ echo ${Foo:-"DefaultValueIfFooIsMissingOrEmpty"} # This works for null (Foo=) and empty string (Foo=""); zero (Foo=0) returns 0. # Note that it only returns default value and doesn't change variable value. +# Brace Expansion { } +# Used to generate arbitrary strings +echo {1..10} +echo {a..z} +# This will output the range from the start value to the end value + # Builtin variables: # There are some useful builtin variables, like echo "Last program's return value: $?" @@ -83,7 +97,7 @@ echo Hello, $Name! # We have the usual if structure: # use 'man test' for more info about conditionals -if [ $Name -ne $USER ] +if [ $Name != $USER ] then echo "Your name isn't your username" else @@ -91,12 +105,12 @@ else fi # NOTE: if $Name is empty, bash sees the above condition as: -if [ -ne $USER ] +if [ != $USER ] # which is invalid syntax # so the "safe" way to use potentially empty variables in bash is: -if [ "$Name" -ne $USER ] ... +if [ "$Name" != $USER ] ... # which, when $Name is empty, is seen by bash as: -if [ "" -ne $USER ] ... +if [ "" != $USER ] ... # which works as expected # There is also conditional execution @@ -130,6 +144,15 @@ ls -l # Lists every file and directory on a separate line # .txt files in the current directory: ls -l | grep "\.txt" +# Since bash works in the context of a current directory, you might want to +# run your command in some other directory. We have cd for changing location: +cd ~ # change to home directory +cd .. # go up one directory + # (^^say, from /home/username/Downloads to /home/username) +cd /home/username/Documents # change to specified directory +cd ~/Documents/.. # still in home directory..isn't it?? + + # You can redirect command input and output (stdin, stdout, and stderr). # Read from stdin until ^EOF$ and overwrite hello.py with the lines # between "EOF": @@ -261,8 +284,11 @@ grep "^foo.*bar$" file.txt grep -c "^foo.*bar$" file.txt # if you literally want to search for the string, # and not the regex, use fgrep (or grep -F) -fgrep "^foo.*bar$" file.txt +fgrep "foobar" file.txt +# trap command allows you to execute a command when a signal is received by your script. +# Here trap command will execute rm if any one of the three listed signals is received. +trap "rm $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM # Read Bash shell builtins documentation with the bash 'help' builtin: help |