Unix AWK String Manipulation

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Compiled by Aluizio using the book UNIX IN A NUTSHELL, Arnold Robbins, O'Reilly Ed., 4th edition, 2005, ISBN 0­596­10029­9. UNIX – awk Programming Language The awk programming language is often used for text and string manipulation within shell scripts,  particularly when input data can be viewed as records and fields. It is also an elegant and capable  programming language that allows you to accomplish a lot with very little work. awk is a pattern­matching program for processing files, especia
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  Compiled by Aluizio using the book UNIX IN A NUTSHELL, Arnold Robbins, O'Reilly Ed., 4 th edition, 2005, ISBN 0-596-10029-9. UNIX – awk Programming Language The awk programming language is often used for text and string manipulation within shell scripts,particularly when input data can be viewed as records and fields. It is also an elegant and capableprogramming language that allows you to accomplish a lot with very little work.awk is a pattern-matching program for processing files, especially when each line has a simple field-oriented layout. Command-Line Syntax: awk [options] 'script' var=value file(s)awk [options] -f filescript var=value file(s) Options: Options Meaning -Ffs Set fs as the field separator.Example:awk -F: '{print $1; print $2; print $3}' /etc/passwd(print the first 3 (colon-separated) fields of each record on separate lines).-v var = value Assign a value to variable before the script begin execution. Simple Pattern-Action Examples:  Pattern-Action Example Meaning {print $1} Print first field of each line. /pattern/ Print all lines that contain pattern. /pattern/ {print $1} Print first field of lines that contain pattern.NF > 2 Select records conataining more than 2 fields.$1 ~ /URGENT/ {print $3, $2} Print fields 2 and 3 in switched order, but only on lineswhose first field matches the string URGENT. /pattern/ {x++}END {print x}Count and print the number of lines matching /pattern/.1  Compiled by Aluizio using the book UNIX IN A NUTSHELL, Arnold Robbins, O'Reilly Ed., 4 th edition, 2005, ISBN 0-596-10029-9. Built-in Variables: Variable Description ARGC Number of arguments on the command-line.ARGV An array containning the command-line arguments, indexed from 0 to ARGC-1.FILENAME Current filename.FS Field Separator (space)NF Number of fields in current record.NR Number of current record.OFS Output field separator (space).ORS Output record separator (newline).$0 Entire input record.$n nth field in current record; fields are separated by FS. Functions:  Functions Description # Ignore all text that follows on the same line.and (exp1, exp2) Return the bitwise AND of exp1 and exp2.break Exit from a while, for, or do loops.continue Begin next iteration of while, for, or do loops.for (init-exp; test-exp; incr-exp)statementC-styling for loop structure. Start from init-exp, incrementingincr-exp value each loop. Executing process until test-expfails.getlinegetline [var] [<file]command | getline [var]Read next line of input.Reads input from file.Reads the output from a command.if (condition)statement1[elsestatement2]If condition is true, do statement1; otherwise, do statement2.or (exp1, exp2) Return the bitwise OR of exp1 and exp2.2  Compiled by Aluizio using the book UNIX IN A NUTSHELL, Arnold Robbins, O'Reilly Ed., 4 th edition, 2005, ISBN 0-596-10029-9.  Functions Description print [output-expr[,...] [dest-expr] Evaluate the output-expr and direct it to standard outputfollowed by the value of OFS (output field separator). Withno output-expr, print $0 (entire line). The output may beredirected to a file or pipe via dest-expr.printf (format [,expr-list]) [dest-expr] Borrowed from the C-language. Allows a formatted output.Example: In line 1, $1 = 5 and $2 = 5.{printf (“Sum of line %d is %d. \n”, NR, $1+$2)}Sum of line 1 is 10.tolower (str) Translate uppercase letters to lowercase.toupper (str) Translate lowercase letters to uppercase. Output Redirections:  Redirection Meaning > file Directs the output to a file, overwriting its previous contents. BE CAREFULusing this redirection.>> file Appends the output to a file, preserving its previous contents.| command Directs the output as the input to a command. 3
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