UNIX Shells by Example (4th Edition)
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| The examples in this section use the following sample database, called datafile , repeated periodically for your convenience. In the database, the input field separator, FS , is whitespace, the default. The number of fields, NF , is 8 . The number may vary from line to line, but in this file, the number of fields is fixed. The record separator, RS , is the newline, which separates each line of the file. Awk keeps track of the number of each record in the NR variable. The output field separator, OFS , is a space. If a comma is used to separate fields, when the line is printed, each field printed will be separated by a space.
6.10.1 Simple Pattern Matching
Example 6.30.
nawk '/west/' datafile northwest NW Joel Craig 3.0 .98 3 4 western WE Sharon Kelly 5.3 .97 5 23 southwest SW Chris Foster 2.7 .8 2 18
EXPLANATION All lines containing the pattern west are printed. Example 6.31.
nawk '/^north/' datafile northwest NW Joel Craig 3.0 .98 3 4 northeast NE TJ Nichols 5.1 .94 3 13 north NO Val Shultz 4.5 .89 5 9
EXPLANATION All lines beginning with the pattern north are printed. Example 6.32.
nawk '/^(noso)/' datafile northwest NW Joel Craig 3.0 .98 3 4 southwest SW Chris Foster 2.7 .8 2 18 southern SO May Chin 5.1 .95 4 15 southeast SE Derek Johnson 4.0 .7 4 17 northeast NE TJ Nichols 5.1 .94 3 13 north NO Val Shultz 4.5 .89 5 9
EXPLANATION All lines beginning with the pattern no or so are printed. 6.10.2 Simple Actions
Example 6.33.
nawk '{print , }' datafile Joel NW Sharon WE Chris SW May SO Derek SE Susan EA TJ NE Val NO Sheri CT
EXPLANATION The output field separator, OFS , is a space by default. The comma between $3 and $2 is translated to the value of the OFS . The third field is printed, followed by a space and the second field.
Example 6.34.
nawk '{print }' datafile JoelNW SharonWE ChrisSW MaySO DerekSE SusanEA TJNE ValNO SheriCT
EXPLANATION The third field is followed by the second field. Because the comma does not separate fields $3 and $2 , the output is displayed without spaces between the fields. Example 6.35.
nawk 'print ' datafile nawk: syntax error at source line 1 context is >>> print <<< nawk: bailing out at source line 1
EXPLANATION This is the nawk (new awk ) error message. Nawk error messages are much more verbose than those of the old awk . In this program, the curly braces are missing in the action statement. Example 6.36.
awk 'print ' datafile awk: syntax error near line 1 awk: bailing out near line 1
EXPLANATION This is the awk (old awk ) error message. Old awk programs were difficult to debug because almost all errors produced this same message. The curly braces are missing in the action statement. Example 6.37.
nawk '{print nawk '{print $0}' datafile northwest NW Joel Craig 3.0 .98 3 4 western WE Sharon Kelly 5.3 .97 5 23 southwest SW Chris Foster 2.7 .8 2 18 southern SO May Chin 5.1 .95 4 15 southeast SE Derek Johnson 4.0 .7 4 17 eastern EA Susan Beal 4.4 .84 5 20 northeast NE TJ Nichols 5.1 .94 3 13 north NO Val Shultz 4.5 .89 5 9 central CT Sheri Watson 5.7 .94 5 13 }' datafile northwest NW Joel Craig 3.0 .98 3 4 western WE Sharon Kelly 5.3 .97 5 23 southwest SW Chris Foster 2.7 .8 2 18 southern SO May Chin 5.1 .95 4 15 southeast SE Derek Johnson 4.0 .7 4 17 eastern EA Susan Beal 4.4 .84 5 20 northeast NE TJ Nichols 5.1 .94 3 13 north NO Val Shultz 4.5 .89 5 9 central CT Sheri Watson 5.7 .94 5 13
EXPLANATION Each record is printed. $0 holds the current record. Example 6.38.
nawk '{print "Number of fields: "NF}' datafile Number of fields: 8 Number of fields: 8 Number of fields: 8 Number of fields: 8 Number of fields: 8 Number of fields: 8 Number of fields: 8 Number of fields: 8 Number of fields: 8
EXPLANATION There are 8 fields in each record. The built-in awk variable NF holds the number of fields and is reset for each record.
6.10.3 Regular Expressions in Pattern and Action Combinations
Example 6.39.
nawk '/northeast/{print , }' datafile TJ NE
EXPLANATION If the record contains (or matches) the pattern northeast , the third field, followed by the second field, is printed. Example 6.40.
nawk '/E/' datafile western WE Sharon Kelly 5.3 .97 5 23 southeast SE Derek Johnson 4.0 .7 4 17 eastern EA Susan Beal 4.4 .84 5 20 northeast NE TJ Nichols 5.1 .94 3 13
EXPLANATION If the record contains an E , the entire record is printed. Example 6.41.
nawk '/^[ns]/{print }' datafile northwest southwest southern southeast northeast north
EXPLANATION If the record begins with an n or s , the first field is printed. Example 6.42.
nawk ' ~ /\.[7-9]+/' datafile southwest SW Chris Foster 2.7 .8 2 18 central CT Sheri Watson 5.7 .94 5 13
EXPLANATION If the fifth field ( $5 ) contains a literal period, followed by one or more numbers between 7 and 9 , the record is printed. Example 6.43.
nawk ' !~ /E/{print , }' datafile northwest NW southwest SW southern SO north NO central CT
EXPLANATION If the second field does not contain the pattern E , the first field followed by the second field ( $1 , $2 ) is printed. Example 6.44.
nawk ' ~ /^Joel/{print " is a nice guy."}' datafile Joel is a nice guy.
EXPLANATION If the third field ( $3 ) begins with the pattern Joel , the third field followed by the string is a nice guy . is printed. Note that a space is included in the string if it is to be printed. Example 6.45.
nawk ' ~ /[0-9][0-9]$/{print }' datafile 23 18 15 17 20 13 13
EXPLANATION If the eighth field ( $8 ) ends in two digits, it is printed.
Example 6.46.
nawk ' ~ /Chin$/{print "The price is $" "."}' datafile The price is .
EXPLANATION If the fourth field ( $4 ) ends with Chin , the string enclosed in double quotes ( "The price is $" ), the eighth field ( $8 ), and the string containing a period are printed. Example 6.47.
nawk '/TJ/{print nawk '/TJ/{print $0}' datafile northeast NE TJ Nichols 5.1 .94 3 13 }' datafile northeast NE TJ Nichols 5.1 .94 3 13
EXPLANATION If the record contains the pattern TJ , $0 (the record) is printed. 6.10.4 Input Field Separators
Use the following datafile2 for Examples 6.48 through 6.52.
Example 6.48.
nawk '{print }' datafile2 Joel Sharon Chris May Derek Susan TJ Val Sheri
EXPLANATION The default input field separator is whitespace. The first field ( $1 ) is printed. Example 6.49.
nawk -F: '{print }' datafile2 Joel Craig Sharon Kelly Chris Foster <more output here> Val Shultz Sheri Watson
EXPLANATION The “F option specifies the colon as the input field separator. The first field ( $1 ) is printed. Example 6.50.
nawk '{print "Number of fields: "NF}' datafile2 Number of fields: 2 Number of fields: 2 Number of fields: 2 <more of the same output here> Number of fields: 2 Number of fields: 2
EXPLANATION Because the field separator is the default (whitespace), the number of fields for each record is 2. The only space is between the first and last name . Example 6.51.
nawk -F: '{print "Number of fields: "NF}' datafile2 Number of fields: 7 Number of fields: 7 Number of fields: 7 <more of the same output here> Number of fields: 7 Number of fields: 7
EXPLANATION Because the field separator is a colon, the number of fields in each record is 7. Example 6.52.
nawk -F"[ :]" '{print , }' datafile2 Joel Craig northwest Sharon Kelly western Chris Foster southwest May Chin southern Derek Johnson southeast Susan Beal eastern TJ Nichols northeast Val Shultz north Sheri Watson central
EXPLANATION Multiple field separators can be specified with nawk as a regular expression. Either a space or a colon will be designated as a field separator. The first and second fields ( $1, $2 ) are printed. (The square brackets must be quoted to prevent the shell from trying to interpret them as shell metacharacters.) 6.10.5 awk Scripting
The following datafile is used for the next example.
Example 6.53.
cat nawk.sc1 # This is a comment # This is my first nawk script 1 /^north/{print , , } 2 /^south/{print "The " " district."} 3 nawk -f nawk.sc1 datafile northwest NW Joel The southwest district. The southern district. The southeast district. northeast NE TJ north NO Val
EXPLANATION
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