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27 Cards in this Set
- Front
- Back
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create a hierarchy of directories (e.g. /tmp/all/my/folders) in one command
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mkdir -p /tmp/all/my/folders
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list a directory in a long format
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ls -l
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remove a directory
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rmdir <directory>
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remove a non-empty directory
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rm -r <dir>
-r for "recursively" |
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show first 5 lines of a file ("head")
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head 5 <file>
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show last 5 lines of a file ("tail")
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tail 5 <file>
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stream the entire file on the screen
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less <file>
Opens Less text editor |
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given a text file, print only the lines containing the letter 'a'
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grep "a" <file>
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list the current directory, showing only the files that have a particular extension (e.g. txt)
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ls *.txt
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count the number of lines in a text file
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wc -l <file>
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count the number of words in a text file
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wc -w <file>
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use redirection to list files, then select only the ones with a specific extension, then count their number
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ls | grep "*.txt"
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use redirection to list files, then select only the ones with a specific extension, then count their number
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ls | grep ".txt" | wc -l
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find all files in your home directory that start with letter "b"
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find ~ -name *.txt -print
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show the manual entry page for a given command
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man <command>
man for Manual |
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show the list of environment variables
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env
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create a new environment variable
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export SEASON=winter
the variable has to be in capitals and there should be no spaces before or after the = sign |
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check that a given environment variable exists
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echo $ENVVAR
Always use $ and all variables are in capitals |
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modify your ~/.bash_profile file to permanently set an env variable and check that it works in a new terminal
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echo "export COUNTRY=uk" >> ~/.bash_profile
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show the permissions for a file
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ls -l | grep <file>
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remove the execute permission for the user and for the group
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chmod ug-x <file>
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add the write permission for the "other"
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chmod o+w <file>
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create a directory and remove the permission that allows you to change into it
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mkdir <dir>
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use the 'echo' command to print "hello, world!" on the screen
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echo hello, world
" " are also fine |
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create a file hello.rb and add the line "puts 'hello, world!'" into it using command line only. Run it by passing its name as an argument to ruby.
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touch hello.rb
echo puts 'hello, world! << hello.rb ruby hello.rb |
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create a file hello.rb and make sure you can execute it by running it directly (hint: you'll need a ruby shebang + specific permissions.
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touch hello.rb
add !#/usr/bin/env ruby to the top of hello.rb chmod u+rwx hello.rb |
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list all processes on the system ("ps" command with some extra flags), find out how many processes of Google Chrome are running using grep and wc
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ps | grep "Google Chrome" | wc -l
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