BASH Cheat Sheet - Level 2: Commands and Operators, Cheat Sheet of Computer Science

Download BASH Cheat Sheet - Level 2: Commands and Operators and more Cheat Sheet Computer Science in PDF only on Docsity! man  command  :  display  the  command’s  manual  page   Jacques  Dainat  -­‐  2015   BASH cheat sheet - Level 2 Miscellaneous \    Escape  character.  It  preserves  the  literal  value  of   the   next   character   that   follows,   with   the   exception  of  newline. `  command`                  The  backtick  (`)  is  a  command  substitution.     echo  The  current  working  directory  is:  `pwd`   >The  current  working  directory  is:  /home/user/path     The  text  between  a  pair  of  backtick  is  executed  by  the   shell   before   the  main   command  and   is   then   replaced   by   the   output   of   that   execution.   The   syntax   $(command)  is  generally  preferable.     $     It   introduces   parameter   expansion,   command   substitution,   or   arithmetic   expansion.   The   parameter    name    or    symbol  to  be  expanded  may   be  enclosed  in  braces.   Using variables variable=value   Assign  a  value  value  to  the  variable  variable.  The   variable  scope  is  restricted  to  the  shell.   local  variable=value   Assign  a  value  value  to  the  local  variable  variable.   It  doesn’t  come  out  a  curly  bracket  area.   export  variable=value   Make   the   variable   name   available   to     the   shell   and  sub-­‐processes.   variable=$(command)       Assign  the  output  of  command  to  variable.   ${#variable} Length  of  the  value  contained  by  the  variable.   ${variable:N}   Keep   the   character   of   the   value   contained   by   variable  after  the  Nth.       ${variable:N:length}   Substring   the   value   contained   by   variable   from   thr  Nth  character  to  up  to  length  specidied.   ${variable/pattern/string}   The  longest  match  of  pattern  against  the  variable   value  is  replaced  with  string.   Print commands echo  My  home  is:  $HOME     Write  arguments  to  the     >My  home  is:  /home/user     standard  output.     echo  –e     Enable   interpretation   of   backslash-­‐ escaped  characters. printf   Format  and  print  the  arguments.     printf  %q  "$IFS"                      Print  the  arguments  shell-­‐quoted.   >'  \t\n'       printf  "%.1f"  2.558     Specify  the  decimal  precision.   >2.6     printf  "%s\t%s\n"  "1"  "2"  "3"  "4"                          %s  interprets  the     >1   2              associated  argument      3   4              literally  as  string.   Using quotes Weak  quoting  -­‐  double  quote  (")  :     string="My  home  is:  $HOME"   echo  $string   >My  home  is:  /home/user   Use   when   you   want   to   enclose   variables   or   use  shell  expansion  inside  a  string.     Strong  quoting  -­‐  single  quote  (')  :     echo  'My  HOME  is:  $HOME'   >My  HOME  is:  $HOME   Preserves   the   literal   value   of   each   character   within  the  quotes.   Wildcards operators Regular  expressions  :   Used  to  match  text.     ^     Matches  the  beginning  of  the  line.   $     Matches  the  end  of  the  line.   ^$   Matches  blank  lines.   .     Any  character.   []     Any  of  the  character  inside  the  brackets.   [^a-­‐f]     Matches  any  character  except  those  in  the  range   a  to  f.   \a     A  letter  (similar  to  [a-­‐zA-­‐Z]).   \t   A  tabulation.   \n     A  new  line.   \w   An  alphanumeric  ([a-­‐zA-­‐Z0-­‐9_])   \W   Non  alphanumeric  (The  opposite  of  \w)   ?         The  preceding  item  matches  0  or  1  time.   *     The  preceding  item  matches  0  or  more  times.   +   The  preceding  item  matches  1  or  more  times.   {N}   The  preceding  item  matches  exactly  N  times.   {N,}   The  preceding  item  matches  N  times  or  more.   {N,M}   The  preceding  item  matches  at  least  N  times  and   not  more  than  M  times.    [:class:]   POSIX   Character   Classes   ([:alnum:],   [:alpha:],   [:blank:],   [:digit:],   etc,   respectively   equivalent   to   A-­‐Za-­‐z0-­‐9,  A-­‐Za-­‐z,  space  or  a  tab,  0-­‐9,  etc).       Globbing  (Pathname  expansion)  :                        Used  to  match  filename(s).   ?   Any  single  character   *   Zero  or  more  characters   []   Specify   a   range.   Any   character   of   the   range   or   none  of  them  by  using  !  inside  the  bracket.   {term1,term2}   Specify   a   list   of   terms   separated   by   commas   and   each   term   must   be   a   name   or   a   wildcard.   {term1..term2}   Called   brace   expansion,   this   syntax   expands  all   the  terms  between  term1  and  term2   (Letters  or  Integers).     With  the  extglob  shell  option  enabled  (check  it  with  shopt)  :   In   the   following  description,  a  pattern-­‐list   is  a   list  of  one   or  more  patterns  separated  by  a  |.