Bash overview

Wildcards

  • * - represents zero or more characters
  • ? - represents a single character
  • [] - represents a range of characters
    • ls [sv]* - looking for a files begins with s or v
    • ls *[0-9]* - set by using a hyphen
    • ls [^a-z]* - caret means not

Permissions

For files: - r read - you may view the contents of the file. - w write - you may change the contents of the file. - x execute - you may execute or run the file if it is a program or script.

For directories: - r - you have the ability to read the contents of the directory (ie do an ls) - w - you have the ability to write into the directory (ie create files and directories) - x - you have the ability to enter that directory (ie cd)

Set for:

  • u user
  • g group
  • o other
  • a all

In case octal mask using, each number represent [ugo].

grep/egrep

  • . (dot) - a single character.
  • ? - the preceding character matches 0 or 1 times only.
  • * - the preceding character matches 0 or more times.
  • + - the preceding character matches 1 or more times.
  • {n} - the preceding character matches exactly n times.
  • {n,m} - the preceding character matches at least n times and not more than m times.
  • [agd] - the character is one of those included within the square brackets.
  • [^agd] - the character is not one of those included within the square brackets.
  • [c-f] - the dash within the square brackets operates as a range. In this case it means either the letters c, d, e or f.
  • () - allows us to group several characters to behave as one.
  • | (pipe symbol) - the logical OR operation.
  • ^ - matches the beginning of the line.
  • $ - matches the end of the line.

flags:

  • -n - display line number as well at the output
  • -c - display quantity of matched lines

Piping and redirection

  • > - STDOUT to a file. cat filename > out
  • < - STDIN from a file. wc -l < filename
  • STDIN and STDOUT. wc -l < barry.txt > myoutput
  • 2> - redirect STDERR
  • ls -l > out 2>&1 redirect STDERR to STDOUT and STDOUT to a file
  • | - pipe. Output of program to the next one. Ex: ls | head -3 | tail -1
  • save the output from the command to the variable - lines=\`cat $1 | wc -l\`

Foreground and Background Jobs

  • program_name & - run program in background
  • ctrl+z - pause the current foreground process and move it into the background
  • jobs - show background jobs
  • fg <job number> - return job to foreground

Commands descriptions

  • “ls [options] [path]“ - list directory contents
    • ls -lahF - long format, all files, human readable format, files indicators
  • “file [path]“ - determine file type
  • “man <command name>“ - access to manual pages
    • man -k <search term> - find required search term in man pages
    • press / to start search inside man page and n to search next result
  • Files manipulations
    • “mkdir [options] <directory>“ - make directories
      • mkdir -p - create parent directories
      • mkdir -v - verbose output
    • “rmdir [options] <directory>“ - remove empty directories. Flags similar to mkdir
    • “touch [options] <filename>“ - change file timestamp. Can be used to create blank file
    • “cp [options] <source> <destination>“ - copy file or directory
      • cp -r <source> <destination> - copy some folder
      • cp -n ... - do not overwrite existing file
    • “mv [options] <source> <destination>“ - move a file or directory
    • “rm [options] <file>“ - remove vile or directory
      • rm -r <directory> - remove non empty directory
      • rm -i <file> - interactive mode
      • rm -d <path> - remove empty directories
  • “cat [files]“ - concatenate and print files
    • cat file1 file2 > out_file - concatenate two files
  • “less <file>“ - display file with navigation. space - next page, b - previous page
  • “chmod [permissions] [path]“ — change file modes or Access Control Lists
    • chmod g+x - add execute permissions to the group
    • chmod u-w - revoke read permissions for the user
    • chmod ug+rx - add read and execute permissions to the user and group
    • chmod 755 - all rights for user, read and execute only for group and other
    • chmod 644 - read/write for user, read only for group and other
  • Filters
    • “head [-number of lines to print] [path]“ - display first lines of a file
    • “tail [-number of lines to print] [path]“ - display the last part of a file
    • “sort [-options] [path]“ - sort lines of text files
    • “nl [-options] [path]“ - line numbering filter
      • nl -s '. ' -w 10 - add some formating
    • “wc [-options] [path]“ - word, line, character, and byte count
    • “cut [-options] [path]“ - cut out selected portions of each line of a file
      • cut -f 1 -d ' ' - get first column from the file, if columns separated by spaces.
      • cut -f 1,2 -d ' ' - get first and second columns
    • “sed <expression> [path]“ - stream editor. basic expression - s/search/replace/g
      • sed 's/oranges/bananas/g' mysampledata.txt - replace oranges with bananas
    • uniq [options] [path] - report or filter out repeated lines in a file
    • tac [path] - concatenate and print files in reverse (reversed cat).
  • diff [options] <files> - compare two files
  • top - display and update sorted information about processes
  • ps - process status
  • date - display current date.
    • date +%F - display in format year-month-day
  • xargs - construct argument list(s) and execute utility
  • find - walk a file hierarchy
    • find . -type f - find all files
    • find . -type d - find all directories
    • find . -size +200M -exec ls -sh {} \ - find and display all files more than 200M
    • find . -mtime -1 - find all recently changed files
  • tar - manipulate tape archives
    • tar -zcvf mytar.tar.gz * - add all files in folder to the archive
    • tar -zxvf mytar.tar.gz - extract files from archive
  • awk ‘pattern { action }’ - pattern-directed scanning and processing language