diff options
Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 205 |
1 files changed, 164 insertions, 41 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index d5d08e9d..211d2944 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -6,6 +6,11 @@ contributors: - ["Darren Lin", "https://github.com/CogBear"] - ["Alexandre Medeiros", "http://alemedeiros.sdf.org"] - ["Denis Arh", "https://github.com/darh"] + - ["akirahirose", "https://twitter.com/akirahirose"] + - ["Anton Strömkvist", "http://lutic.org/"] + - ["Rahil Momin", "https://github.com/iamrahil"] + - ["Gregrory Kielian", "https://github.com/gskielian"] + - ["Etan Reisner", "https://github.com/deryni"] filename: LearnBash.sh --- @@ -27,64 +32,93 @@ echo Hello world! echo 'This is the first line'; echo 'This is the second line' # Declaring a variable looks like this: -VARIABLE="Some string" +Variable="Some string" # But not like this: -VARIABLE = "Some string" -# Bash will decide that VARIABLE is a command it must execute and give an error -# because it couldn't be found. +Variable = "Some string" +# Bash will decide that Variable is a command it must execute and give an error +# because it can't be found. + +# Or like this: +Variable= 'Some string' +# Bash will decide that 'Some string' is a command it must execute and give an +# error because it can't be found. (In this case the 'Variable=' part is seen +# as a variable assignment valid only for the scope of the 'Some string' +# command.) # Using the variable: -echo $VARIABLE -echo "$VARIABLE" -echo '$VARIABLE' +echo $Variable +echo "$Variable" +echo '$Variable' # When you use the variable itself — assign it, export it, or else — you write -# its name without $. If you want to use variable's value, you should use $. +# its name without $. If you want to use the variable's value, you should use $. # Note that ' (single quote) won't expand the variables! # String substitution in variables -echo ${VARIABLE/Some/A} -# This will substitute the first occurance of "Some" with "A" +echo ${Variable/Some/A} +# This will substitute the first occurrence of "Some" with "A" # Substring from a variable -echo ${VARIABLE:0:7} +Length=7 +echo ${Variable:0:Length} # This will return only the first 7 characters of the value # Default value for variable -echo ${FOO:-"DefaultValueIfFOOIsMissingOrEmpty"} -# This works for null (FOO=), empty string (FOO=""), zero (FOO=0) returns 0 +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. # Builtin variables: # There are some useful builtin variables, like -echo "Last program return value: $?" +echo "Last program's return value: $?" echo "Script's PID: $$" -echo "Number of arguments: $#" -echo "Scripts arguments: $@" -echo "Scripts arguments seperated in different variables: $1 $2..." +echo "Number of arguments passed to script: $#" +echo "All arguments passed to script: $@" +echo "Script's arguments separated into different variables: $1 $2..." # Reading a value from input: echo "What's your name?" -read NAME # Note that we didn't need to declare a new variable -echo Hello, $NAME! +read Name # Note that we didn't need to declare a new variable +echo Hello, $Name! # We have the usual if structure: # use 'man test' for more info about conditionals -if [ $NAME -ne $USER ] +if [ $Name -ne $USER ] then - echo "Your name is your username" -else echo "Your name isn't your username" +else + echo "Your name is your username" fi +# NOTE: if $Name is empty, bash sees the above condition as: +if [ -ne $USER ] +# which is invalid syntax +# so the "safe" way to use potentially empty variables in bash is: +if [ "$Name" -ne $USER ] ... +# which, when $Name is empty, is seen by bash as: +if [ "" -ne $USER ] ... +# which works as expected + # There is also conditional execution echo "Always executed" || echo "Only executed if first command fails" echo "Always executed" && echo "Only executed if first command does NOT fail" +# To use && and || with if statements, you need multiple pairs of square brackets: +if [ "$Name" == "Steve" ] && [ "$Age" -eq 15 ] +then + echo "This will run if $Name is Steve AND $Age is 15." +fi + +if [ "$Name" == "Daniya" ] || [ "$Name" == "Zach" ] +then + echo "This will run if $Name is Daniya OR Zach." +fi + # Expressions are denoted with the following format: echo $(( 10 + 5 )) -# Unlike other programming languages, bash is a shell — so it works in a context -# of current directory. You can list files and directories in the current +# Unlike other programming languages, bash is a shell so it works in the context +# of a current directory. You can list files and directories in the current # directory with the ls command: ls @@ -96,12 +130,45 @@ ls -l # Lists every file and directory on a separate line # .txt files in the current directory: ls -l | grep "\.txt" -# You can also redirect a command, input and error output. -python2 hello.py < "input.in" -python2 hello.py > "output.out" -python2 hello.py 2> "error.err" -# The output error will overwrite the file if it exists, if you want to -# concatenate them, use ">>" instead. +# You can redirect command input and output (stdin, stdout, and stderr). +# Read from stdin until ^EOF$ and overwrite hello.py with the lines +# between "EOF": +cat > hello.py << EOF +#!/usr/bin/env python +from __future__ import print_function +import sys +print("#stdout", file=sys.stdout) +print("#stderr", file=sys.stderr) +for line in sys.stdin: + print(line, file=sys.stdout) +EOF + +# Run hello.py with various stdin, stdout, and stderr redirections: +python hello.py < "input.in" +python hello.py > "output.out" +python hello.py 2> "error.err" +python hello.py > "output-and-error.log" 2>&1 +python hello.py > /dev/null 2>&1 +# The output error will overwrite the file if it exists, +# if you want to append instead, use ">>": +python hello.py >> "output.out" 2>> "error.err" + +# Overwrite output.out, append to error.err, and count lines: +info bash 'Basic Shell Features' 'Redirections' > output.out 2>> error.err +wc -l output.out error.err + +# Run a command and print its file descriptor (e.g. /dev/fd/123) +# see: man fd +echo <(echo "#helloworld") + +# Overwrite output.out with "#helloworld": +cat > output.out <(echo "#helloworld") +echo "#helloworld" > output.out +echo "#helloworld" | cat > output.out +echo "#helloworld" | tee output.out >/dev/null + +# Cleanup temporary files verbosely (add '-i' for interactive) +rm -v output.out error.err output-and-error.log # Commands can be substituted within other commands using $( ): # The following command displays the number of files and directories in the @@ -113,7 +180,7 @@ echo "There are $(ls | wc -l) items here." echo "There are `ls | wc -l` items here." # Bash uses a case statement that works similarly to switch in Java and C++: -case "$VARIABLE" in +case "$Variable" in #List patterns for the conditions you want to meet 0) echo "There is a zero.";; 1) echo "There is a one.";; @@ -121,14 +188,34 @@ case "$VARIABLE" in esac # for loops iterate for as many arguments given: -# The contents of var $VARIABLE is printed three times. -for VARIABLE in {1..3} +# The contents of $Variable is printed three times. +for Variable in {1..3} do - echo "$VARIABLE" + echo "$Variable" +done + +# Or write it the "traditional for loop" way: +for ((a=1; a <= 3; a++)) +do + echo $a +done + +# They can also be used to act on files.. +# This will run the command 'cat' on file1 and file2 +for Variable in file1 file2 +do + cat "$Variable" +done + +# ..or the output from a command +# This will cat the output from ls. +for Output in $(ls) +do + cat "$Output" done # while loop: -while [true] +while [ true ] do echo "loop body here..." break @@ -152,17 +239,53 @@ bar () } # Calling your function -foo "My name is" $NAME +foo "My name is" $Name # There are a lot of useful commands you should learn: -tail -n 10 file.txt # prints last 10 lines of file.txt -head -n 10 file.txt +tail -n 10 file.txt # prints first 10 lines of file.txt -sort file.txt +head -n 10 file.txt # sort file.txt's lines -uniq -d file.txt +sort file.txt # report or omit repeated lines, with -d it reports them -cut -d ',' -f 1 file.txt +uniq -d file.txt # prints only the first column before the ',' character +cut -d ',' -f 1 file.txt +# replaces every occurrence of 'okay' with 'great' in file.txt, (regex compatible) +sed -i 's/okay/great/g' file.txt +# print to stdout all lines of file.txt which match some regex +# The example prints lines which begin with "foo" and end in "bar" +grep "^foo.*bar$" file.txt +# pass the option "-c" to instead print the number of lines matching the regex +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 + + +# Read Bash shell builtins documentation with the bash 'help' builtin: +help +help help +help for +help return +help source +help . + +# Read Bash manpage documentation with man +apropos bash +man 1 bash +man bash + +# Read info documentation with info (? for help) +apropos info | grep '^info.*(' +man info +info info +info 5 info + +# Read bash info documentation: +info bash +info bash 'Bash Features' +info bash 6 +info --apropos bash ``` |