CEG 233: Linux and Windows

Cheat Sheet

Bash and PowerShell • File Name RegEx
String Matching RegEx • String Replacement RegEx

Bash and PowerShell Quick Reference

Bash PowerShell Description
Scripting Basics
#!/bin/bash
"shebang" as the first line of the file.  Give execute permission on script file. Suggested ext: .sh		 .ps1 extension. For downloaded scripts, unblock the file under file properties in Windows Explorer. Steps for making scripting files run. In PowerShell, the first time you do scripting, run PowerShell as administrator and type set-executionpolicy remotesigned.
source (or) . . shell built-in: execute the commands in a file
echo String echo String (or)
Write-Host String		 Prints String to the screen. In PowerShell, Write-Host forces the output to the screen instead of being a return value.
x=4
(No spaces around =)		 $x = 4 Creates a variable and assigns it a 4. In Bash, do not put white space around the equals sign, and do not use a $ in the LHS.
let x=$y+5 (or)
x=$(( $y + 5 ))		 $x = $y + 5 To x assign the value of y plus 5.
# comment # comment A comment 
pfm() {
  echo arg1 $1 arg2 $2
}
 
function pfm($a, $y) {
  echo arg1 $a arg2 $y
}
 defining procedure/function/method pfm with two arguments; does not call it.
pfm hello there pfm hello there calling pfm and passing args
x=$(cmd a1 a2 a3) $x=cmd a1 a2 a3 stdout of cmd a1 a2 a3 assigned to var x
r5() {
   return 5
}

r5
v=$?		 function r5 {
   echo 5  (or)  return 5
}

$v = r5		 The return value of a Bash function is stored in the variable $?.
Strings
= != -eq -ne -ceq -cne String comparisons. In Bash, be sure that the strings literals are in quotes.
  "" | gm Get a list of non-static string members
  [string] | gm -static Get a list of static string members
${string#text_to_remove} string.TrimStart("characters") Removes the specified characters/text from the beginning of the string.
${string%text_to_remove} string.TrimEnd("characters") Removes the specified characters/text from the end of the string.  Suppose $fnm == helloThere.txt; then ${fnm%.???} is helloThere
Pattern Matching
grep select-string print lines matching a pattern
sed -replace performs string transformations
Booleans and Conditions
true  false $true  $false Boolean literals
-lt -gt -le -ge -eq -ne -lt -gt -le -ge -eq -ne Arithmetic relational operators
  -like True if a string matches a wildcard pattern
  -match True if a string matches a regular expressions
  Where-Object { condition } Used to filter input by a condition. Remember that $_ refers to the current object being tested.
-z $var $var -eq $null True if $var is null
-n $var $var -ne $null True if $var is not null (contains one or more characters)
-o -a -or -and Logical or and and
-e file Test-Path file True if file exists.
! -e file ! (Test-Path file) True if file does not exist.
-d file file.PSISContainer True if file is a directory. In PowerShell, if file is not a file variable, be sure to get the file object first with gi.
-s file   True if file exists and has a size greater than zero.
file1 -nt file2   True if file1 is newer (according to modification date) than file2
file1 -ot file2   True if file1 is older (according to modification date) than file2
Control Structures
if [ condition ]
then
   codeblock
fi		 if (condition) {
   codeblock
}		 If statement. In Bash, be sure to leave a space between the condition and the bracket.
if [ condition ]
then
   codeblock
elif [ condition ]
then
   codeblock
else
   codeblock
fi		 if (condition) {
   codeblock
}
elseif (condition) {
   codeblock
}
else {
   codeblock
}		 If - else if - else statement
var=0
while [ $var -lt 10 ]
do
   echo $var
   var=$(( $var + 1 ))
done		 $var = 0
while ($var -lt 10) {
   echo $var
   $var++
}		 Prints numbers 0 through 9.
for ((i=0; i < 10; i++)) do
   echo $i
done		 for ($i=0;$i -lt 10; $i++)
{
   echo $i
}		 Prints numbers 0 through 9.
for var in $array
do
   codeblock
done		 foreach ($var in $array)
{
   codeblock
}		 For each loop
continue  break continue  break Loop controls: continue stops current loop iteration and begins the next; break exits the loop currently being executed.
basename file file.name The name of file without the path. In PowerShell, remember to first get the file object.
dirname file file.directoryname The name directory file is in. In PowerShell, remember to first get the file object.
stat -c%s $file (or)
$(stat -c%s $file)		 file.length The number of bytes in file. In PowerShell, remember to first get the file object.
  file.LastWriteTime The last modified time for file. Remember to first get the file object.
files=`ls` (or)
files=$(ls) (or)
files=*		 $files = Get-Item * Store a list of the files in the current working directory in $files. In PowerShell, check out the -exclude flag as well as the Get-ChildItem cmdlet.
|  >  >>  2>  2>> |  >  >>  2>  2>> Piping, output and error redirection. In Bash, output redirected to /dev/null is gone. In PowerShell, output redirected to $null is gone.
File Information/Operations
ls   Listing of files. For Bash, learn the options of -lisa, -r, -R.
  ls Listing of files. For PowerShell, learn -f, -r, -filter, and -exclude
tree tree Graphically displays the directory structure of a drive or path.
cat cat List the contents of a file on the stdout
more more List the contents of a file on the stdout, pausing after each page
mkdir mkdir Creates a directory.
rmdir rmdir Deletes a folder if it is empty
pwd pwd print working directory
cd cd Change the current directory to the one given as argument.
pushd pushd Saves the current directory name on the stack, and then cd's the one given as argument.
popd popd Pop off the top-most name on the stack, and then cd to it
mv mv Moves or renames files. In PowerShell, check out the -force and -WhatIf flags. In Bash, check out the -f flag.
cp -r cp -r Copies files and directory trees recursively.
cp cp Copies files. In PowerShell, check out the -force and -WhatIf flags. In Bash, check out the -f flag.
rm rm Deletes a file. Check out the -r flag. In PowerShell, check out the -force and -WhatIf flags. In Bash, check out the -f flag.
cat cat show the contents of each file in sequence
more more pagination
rm rm Remove files
ln   Link (hard or soft) to an existing file.
  mklink Link (hard or soft) to an existing file. Type cmd /c mklink to use it in PowerShell
chmod attrib Change file permissions/attributes
icacls Displays or modifies access control lists (ACLs) of files
chown icacls Change ownership of a file. In PowerShell, multiple steps are necessary
umask get/set the file mode creation mask; packed vector of bits controlling the initial permissions on a newly created file
du measure Disk space Used. In PowerShell, try gci . -r | measure -property length -sum
wc Measure-Object word count, etc.
od Octal dump of file content. Almost always used with -x for hexadecimal dump
tr Translate/substitute characters; useful in improving interoperability
assoc List associations of commands with extensions. Type cmd /c assoc to use it in PowerShell
file Heuristically determine the type of file content
grep select-string Search for a string in a file's content. For now, learn it without regexp.
find gci Locate a file. By name, etc. For now, learn it without regexp.
which   Gives the full path name of a command
  where Gives the full path name of a command.  Type cmd /c where to use it in PowerShell
diff diff List the differences between two text files
cmp compare show the differences between two files
  gci . -r | sort length -descending | select -first 10 get a list of the 10 largest files in the current directory (recursive)
vi vim A powerful text editor. For now, learn to edit simple text files with it.
kate, leafpad notepad Simple text editors.
emacs emacs A very powerful multi-purpose text editor. For now, learn to edit simple text files with it.
Processes
ps ps shows current processes
  gps | sort ws | select -last 5 Get a list of the 5 processes using the most memory
  gsv | where {$_.Status -eq "Stopped"} Get a list of stopped services
top   like ps, but with continuous updates
bg   place a STOPped process in the background
fg   bring a backgrounded process to foreground
kill kill kills a running program
ltrace   show lib calls made
strace   show sys calls made
time cmd a1 a2 Measure-Command times commands, etc.
nice cmd a1 a2 start /low cmd a1 a2 lower the priority and run cmd a1 a2
System
man man show reference pages
set set set the values of shell variables
set (with no args) gv get and show the values of shell variables
env ls env: lists the current environment variables
$PATH $env:path the search path
sftp, filezilla filezilla transfer files securely to/from a remote machine
ssh, putty sshclient, putty remote login securely
w   who is on the system, and what they are doing
df gdr show mounted volumes, etc.

File Name Regular Expressions

http://www.cs.wright.edu/~pmateti/Courses/233/Labs/RegEx/RegExLab.html

File-name-regex are used by shells in the context of file names.

Meta Meaning Example Matches
* Match zero or more characters a*txt "atxt", "aa.txt", "abtxt", "aba.txt", etc
? Match exactly one character ?.txt "a.txt", "b.txt", etc. NOT "aa.txt" or "ab.txt".
. not a meta char . matches itself
!history meta char!ca command in your history that begins with c.
$value of a var$HOMEnot a file name thing, but ...
#comment line# this is just a comment
%cut out matching tail${fnm%.mp3} $fnm but without the .mp3 tail
#cut out matching head${fnm#*.} $fnm but without the head substring matching *.
'use as-is'*'the quote-stripped single token * as-is
"expand but protectls -i "$fnm"value of $fnm; useful when $fnm has e.g. blanks
`execute cmd enclosedls -l `cat list.txt` and subst resulting stdout
()grouping of cmds(echo start; ls -lisa; echo done) | wc -l
[]as in string regex[d-h]any one of d,e,f,g,h
{}enumerationecho {hello,hi}there

String Matching RegEx

from http://www.cheatography.com/davechild/cheat-sheets/regular-expressions/

Regular Expressions Anchors

^ Start of string
\A Start of string
$ End of string
\Z End of string
\b Word boundary
\B Not word boundary
\< Start of word
\> End of word

Regular Expressions Character Classes

\c Control character
\s White space
\S Not white space
\d Digit
\D Not digit
\w Word
\W Not word
\x Hexadecimal digit
\O Octal digit

Regular Expressions Assertions

?= Lookahead assertion
?! Negative lookahead
?<= Lookbehind assertion
?!= or ?<! Negative lookbehind
?> Once-only Subexpression
?() Condition [if then]
?()| Condition [if then else]
?# Comment
  

Regular Expressions Quantifiers

There must be a regex to the left of these.

* 0 or more
+ 1 or more
? 0 or 1
{3} Exactly 3
{3,} 3 or more
{3,5} 3, 4 or 5

Add a ? to a quantifier to make it ungreedy.

Regular Expression Common Metacharacters

^ [ .
$ { *
( \ +
) | ?
< >  

The escape character is usually the backslash - \.

Regular Expressions Special Characters

\n New line
\r Carriage return
\t Tab
\v Vertical tab
\f Form feed
\xxx Octal character xxx
\xhh Hex character hh
 

Regular Expressions Groups and Ranges

. Any character except new line (\n)
(a|b) a or b
(...) Group
(?:...) Passive (non-capturing) group
[abc] Range (a or b or c)
[^abc] Not a or b or c
[a-q] Letter from a to q
[A-Q] Upper case letter from A to Q
[0-7] Digit from 0 to 7
\n nth group/subpattern

Ranges are inclusive.

Regular Expressions Pattern Modifiers

g Global match
i Case-insensitive
m Multiple lines
s Treat string as single line
x Allow comments and white space in pattern
e Evaluate replacement
U Ungreedy pattern

String Replacement RegEx

$n nth non-passive group
$2 "xyz" in /^(abc(xyz))$/
$1 "xyz" in /^(?:abc)(xyz)$/
$` Before matched string
$' After matched string
$+ Last matched string
$& Entire matched string

Some regex implementations use \ instead of $.

URL of this file: http://www.cs.wright.edu/~pmateti/Courses/233/Top/233-CheatSheet.html