Here is a quick guide to nawk. nawk as it has more functionalities over awk. Most systems now would have both programs installed. See also:

• Quick guide to n8n
• Quick guide to NSCC ASPIRE2A
• Quick guide to Docker
• Quick guide to CVS
• Quick guide to GNUPlot
• Quick guide to Emacs
• Quick guide to Git

To run nawk

• From command line : nawk ‘program’ inputfile1 inputfile2 …
• From a file : nawk -f programfile inputfile1 inputfile2 …

Structure of nawk program

• A nawk program can consist of three sections: nawk ‘BEGIN{…}{… /* BODY */ …}{END}’ inputfile
• Both ‘BEGIN’ and ‘END’ blocks are optional and are executed only once.
• The body is executed for each line in the input file.

Field Separators

• The following example adds the field ‘=’ separator, in addition to the blank space separator: nawk ‘BEGIN{FS = ” *|=”}{print $2}’ input file.
• For example, if the input file contains the line “Total = 500”, then the output will be 500.

Printing Environment Variables

• The following example appends the current path to a list of filenames/directories:
  ls -alg | nawk ‘{print ENVIRON[“$PWD”] “/” $8}’
  
• ENVIRON is an array of environment variables indexed by the individual variable name.
  
• The variable FILENAME is a string that stores the current name of the file nawk is parsing.

Examples of usage

• To kill all the jobs of the current user : kill -9 `ps -ef | grep $LOGNAME | nawk ‘{print $2}’`

Multi-dimensional array

• To use 2D or multi-dimensional array, use comma to seperate the array index: matrix[3, 5] = $(i+5)

Another examples

• The example below calculates the averages for 16 items from 10 sets of readings.
• Example of an input line the program is trying to match: Total elapsed time is 560

BEGIN{
  printf("--------- Execution Time -----------\n");
  item=16;
  set=10;
}
{# all new variables are initialized to 0for(;j < set;j++)
  for(i=0;i < item; i++)
  {# skip input until the second word matches "elapsed"while($2 != "elapsed")
  getline;# notice the use of array without declaring its# dimensionsum[i]+=$5;
getline;
  }

if(j==set){for(i=0;i < item;i++){
   
  # this and the next 2 lines are comments
  # you can use either print or printf for output 
  # print sum[i]/set;
   
  printf("Set %d : %6.3f\n",i,sum[i]/set);
}
j++;
  }
}END{
  printf("-------------- End --------------");
}

Examples from the man page

• Write to the standard output all input lines for which field 3 is greater than 5:
  $3 > 5
  
• Write every tenth line:
  (NR % 10) == 0
  
• Write any line with a substring matching the regular expression:
  /(G|D)(2[0-9][[:alpha:]]*)/
  
• Print any line with a substring containing a G or D, followed by a sequence of digits and characters:
  /(G|D)([[:digit:][:alpha:]]*)/
  
• Write any line in which the second field contains a backslash:
  $2 ~ /\\/
  
• Write any line in which the second field contains a backslash (alternate method). Note that backslash escapes are interpreted twice, once in lexical processing of the string and once in processing the regular expression.
  $2 ~ “\\\\”
  
• Write the second to the last and the last field in each line, separating the fields by a colon:
  {OFS=”:”;print $(NF-1), $NF}
  
• Write lines longer than 72 characters:
  {length($0) > 72}
  
• Write the first two fields in opposite order separated by the OFS:
  { print $2, $1 }
  
• Same, with input fields separated by comma or space and tab characters, or both:
  BEGIN { FS = “,[\t]*|[\t]+” }{ print $2, $1 }
  
• Add up first column, print sum and average:
  {s += $1 }END{print “sum is “, s, ” average is”, s/NR}
  
• Write fields in reverse order, one per line (many lines out for each line in):
  { for (i = NF; i > 0; –i) print $i }
  
• Write all lines between occurrences of the strings “start” and “stop”:
  /start/, /stop/
  
• Write all lines whose first field is different from the previous one:
  $1 != prev { print; prev = $1 }
  
• Simulate the echo command:
  BEGIN { for (i = 1; i < ARGC; ++i) printf “%s%s”, ARGV[i], i==ARGC-1?”\n”:””}
  
• Write the path prefixes contained in the PATH environment variable, one per line:
  BEGIN{n = split (ENVIRON[“PATH”], path, “:”) for (i = 1; i <= n; ++i) print path[i]}

Here is a quick guide to setting up and using CVS. The commands shown below were tested on Concurrent Versions System (CVS) 1.10 available from Cyclic Software.

See also:

• Quick guide to GNUPlot
• Quick guide to n8n
• Quick guide to Docker
• Quick guide to nawk
• Quick guide to Emacs
• Quick guide to Git

Setup

• Set CVSROOT to a directory (e.g. setenv CVSROOT ~/cvsroot )
• Run “cvs init”

Put Project into CVS

• To add version control for a project consist of multiple files in a directory, e.g. ~/project
• cd to ~/project
• Run “cvs import -m “Project” myproject sample start”
• The respective arguments are :
• cvs -m “Log message” repository vendor-tag release-tags
• You can put anything you like for the tags and log message.
• You will need to use “repository” to checkout your files later.

Checkout a Project

• To checkout a project
• Run “cvs checkout myproject”
• You can subsitute “myproject” for any other repositories in the CVS.

Update a Project

• To update a project after modifying several files
• Run “cvs commit”
• An editor will be shown to allow you to add comments on the changes
• To use another editor eg: xemacs, do “setenv EDITOR xemacs”

Add/Remove File

• To add a file, run “cvs add filename; cvs commit”
• To remove a file, run “cvs remove filename; cvs commit”

Topics not covered here

• Version branches
• Multiple developers

See also this site for a more comprehensive tutorial.