Godot's System Utilities

Tips For Awk

# prepend and append some text on each line of a text file:

 awk '{print "prefix "$1" postfix"}' input.txt > /tmp/output.txt

# replace the value of the second column in file1.dat by zero if it is strictly less than 0.1 (cfr., the gnuplot manual):
```
 awk '{print $1,($2<0.1) ? 0.0 : $2}' file1.da 
```
# multiply the numeric value of the second column in file1.dat by five if the value of the first column is in the range of [1,3] (cfr., the gnuplot manual):
```
 awk '{print $1,($1<=3 && $1>=1)? $2*5 : $2}' file1.dat 
```

Tips For MyHowTos

# text processing:

# convert characters from lower to upper case:
```
 fortune | tr [:upper:] [:lower:] 
```

# finding out how many times a particular item, in this case a dot, occurs on a text line

 for a in `cat /tmp/file.txt`; do
  nof=$[`echo $a|sed s/'\.'/'\n'/g|wc -l` -1]
  echo  a . occurs $nof times in $a
 done

# unescaping escaped text/html/javascript/... found in a file $LOGFILE:

 cat $LOGFILE|sed s/+/' '/g|sed s/%0D%0A/" -- "/g|sed s/%20/" "/g|sed s/%21/'!'/g|\
sed s/%22/'"'/g|sed s/%23/'\#'/g|sed s/%24/"$"/g|sed s/%25/"%"/g|sed s/%26/"\&"/g|sed s/%27/"'"/g|\
sed s/%28/'('/g|sed s/%29/')'/g|sed s/%2A/'*'/g|sed s/%2B/'+'/g|sed s/%2C/','/g|sed s/%2D/'-'/g|\
sed s/%2E/'.'/g|sed s/%2F/'\/'/g|sed s/%3A/':'/g|sed s/%3B/';'/g|sed s/%3C/'<'/g|sed s/%3D/'='/g|\
sed s/%3E/'>'/g|sed s/%3F/'?'/g|sed s/%40/'@'/g|sed s/%5B/'['/g|sed s/%5C/'\\'/g|sed s/%5D/']'/g|\
sed s/%5E/'^'/g|sed s/%5F/'_'/g|sed s/%60/'`'/g|sed s/%7B/'{'/g|sed s/%7C/'|'/g|sed s/%7D/'}'/g|\
sed s/%7E/'~'/g|sed s/%D3/'<'/g

# a very nice overview of commonly used text processing commands can be found at http://www.tldp.org/LDP/abs/html/textproc.html
# remove all blank lines from a file:
```
 grep -v '^$' input.txt > output.txt 
```
# count the number of newlines, words and bytes in a text file:
```
 wc input.txt 
```
# reverse all the lines in a file:
```
 rev file.txt 
```

# searching for specific patterns using grep and regular expressions (mostly copied from http://www.robelle.com/library/smugbook/regexpr.html):

# the theory:

 ^ (Caret)        =    match expression at the start of a line, as in ^A.
 $ (Question)     =    match expression at the end of a line, as in A$.
 \ (Back Slash)   =    turn off the special meaning of the next character, as in \^.
 [ ] (Brackets)   =    match any one of the enclosed characters, as in [aeiou].
                       Use Hyphen "-" for a range, as in [0-9].
 [^ ]             =    match any one character except those enclosed in [ ], as in [^0-9].
 . (Period)       =    match a single character of any value, except end of line.
 * (Asterisk)     =    match zero or more of the preceding character or expression.
 \{x,y\}          =    match x to y occurrences of the preceding.
 \{x\}            =    match exactly x occurrences of the preceding.
 \{x,\}           =    match x or more occurrences of the preceding.

# examples:

 cat -v -e -t dump                           # show non-printing characters too
 grep BOB tmpfile                        # search 'tmpfile' for 'BOB' anywhere in a line
 grep -i -w blkptr *                     # case insensitive search all files in the current directory for the word blkptr
 grep run[- ]time *.txt                  # find 'run time' or 'run-time' in all txt files
 grep smug files                         # search files for lines with 'smug'
 grep '^smug' files                      # 'smug' at the start of a line
 grep 'smug$' files                      # 'smug' at the end of a line
 grep '^smug$' files                     # lines containing only 'smug'
 grep '\^s' files                        # lines starting with '^s', "\" escapes the ^
 grep '[Ss]mug' files                    # search for 'Smug' or 'smug'
 grep 'B[oO][bB]' files                  # search for BOB, Bob, BOb or BoB 
 grep '^$' files                         # search for blank lines
 grep '[0-9][0-9]' file                  # search for pairs of numeric digits
 grep '^From: ' /var/spool/mail/$USER    # list your mail
 grep '[a-zA-Z]'                         # any line with at least one letter
 grep '[^a-zA-Z0-9]                      # anything not a letter or number
 grep '[0-9]\{3\}-[0-9]\{4\}'            # 999-9999, like phone numbers
 grep '^.$'                              # lines with exactly one character
 grep '"smug"'                           # 'smug' within double quotes
 grep '"*smug"*'                         # 'smug', with or without quotes
 grep '^\.'                              # any line that starts with a Period "."
 grep '^\.[a-z][a-z]'                    # line start with "." and 2 lc letters

# file processing:
1. # count the number of times a particular character (in the example a comma) occurs in some file:
```
 cat file.txt | tr -c -d ',' | wc -c 
```
2. # character set translator -- translates character sets from one encoding to another (utf-8, ascii, iso 8859-[123456789], unicode, msdos,...):
```
 tcs 
```
3. # make a hexdump or do the reverse:
```
 xxd file > file.hex
 xxd -r file.hex > file.bis 
```
4. # dump a file byte per byte using octet, decimal, hex or binary notation:
```
 od -j 2 -t x1 file > file.hex 
```
5. # replace all spaces in all relevant file names by underscores:
```
 find . -name \*' '\* -exec rename s/' '/_/g "{}" \; 
```
6. # strip the path from a filename, or the last part of an absolute path:
```
 basename extendedFilename; dirname extendedFilename 
```
7. # find all files that are between 100 and 50 days old:
```
 find . -mtime +50 -mtime -100 -daystart 
```
# process processing:
1. # redirect stderr to stdout:
```
 buggyProg 2>&1 
```
2. # redirect stdout to stderr:
```
 buggyProg 1>&2 
```
3. # redirect both stderr and stdout to a file:
```
 buggyProg &> file 
```

Tips To Use Cvs

# checkout of a cvs module from a cvs server with respect to a particular date:

 cvs -z3 -d :pserver:cvs@cvs.server.org:/pub/cvsroot checkout -D "month dd yyyy" module

Tips To Use Diff And Patch

# the following command produces (given two source trees ~/original/sources and ~/updated/sources) an overview of the differences between these two trees:
```
 cd ~/original/sources
 tar -xzvf ~/whatever.tgz
 cd ~
 diff -ruN original/sources updated/sources > how.to.patch.original.sources
```
# the following command produces, given the original source tree and the differences between the original and updated sources, updated sources:
```
 cd ~/current/sources
 tar -xzvf ~/whatever.tgz
 patch -p2 < how.to.patch.original.sources
```

Setting Up An Encrypted Filesystem

# http://loop-aes.sourceforge.net/loop-AES.README
# Encryption HOWTO
# Encrypted Root Filesystem HOWTO
# Cryptoloop HOWTO
# Setting up the Cryptographic FileSystem (cfs):
1. # setting the thing up:
  1. # install the cfs package:
```
 sudo apt-get install cfs 
```
  2. # create /etc/exports if it does not yet exist to avoid cfsd's complaints:
```
 sudo touch /etc/exports 
```
  3. # start the cfs daemon:
```
 sudo /etc/init.d/cfsd restart 
```
2. # using the stuff:
  1. # prepare the creation of an encrypted directory called "~/encrDir":
```
 cmkdir ~/encrDir 
```
    # the cmkdir command prompts for a strong passphrase (of at least 16 characters)
  2. # make this directory available to the user with that password:
```
 cattach ~/encrDir decrypted 
```
    # the cattach command prompts for the passphrase that was used to create the directory ~/encrDir # once completed, the directory /crypt/decrypted becomes available wherein one can edit all files in plaintext
  3. # once you finish editing the decrypted data, this directory should be unmounted:
```
 cdetach decrypted 
```
    # note that the content of the directory ~encrDir is at all times encrypted. The plaintext is only available to the user who presented the correct passphrase

Tips For Mysql

# setting the server root password:

 mysql -uroot mysql
 mysql>UPDATE user SET Password=PASSWORD('mysqlrootpassword') WHERE user='root';
 mysql>FLUSH PRIVILEGES;
 mysql>quit

# initial setting up of diogenes:

 mysql -uroot -p"mysqlrootpassword"
 mysql> use diogenes;
 mysql> insert into diogenes_auth set username="root",password=MD5(""),perms="admin";
 mysql> quit

Tips For Perl

# look for a specific pattern in standard input (binary or text files) and print the pattern's byte-offset:

#!/usr/bin/perl
open(P,"-");
$a=join("",<P>);
while($a =~ m/pattern/gs){
        print join(/:/,@-)."\n";
        }
close(P);

# find all common lines in two files (cfr., http://perlmonks.thepen.com/36725.html):
```
 perl -ne 'print if ($seen{$_} .= @ARGV) =~ /10$/' fileA fileB >output 
```

Tips For Sed

# have sed fetch all lines from a text file starting from the sixth line:
```
 sed -n '6,$p' file.txt 
```
# append line i to line i+1 if line i+1 starts with $PATTERN:
```
 sed ':a;N;$!ba;s/\n$PATTERN/$PATTERN/g' file.txt 
```
# a list of handy one-liners for the unix stream editor sed can be found at http://www.student.northpark.edu/pemente/sed/sed1line.txt