Shell Script espressioni utili AWK

HANDY ONE-LINERS FOR AWK                                  22 July 2003

compiled by Eric Pement            version 0.22

Latest version of this file is usually at:

http://www.student.northpark.edu/pemente/awk/awk1line.txt

USAGE:

Unix:  awk '/pattern/ {print "$1"}'    # standard Unix shells

DOS/Win:  awk '/pattern/ {print "$1"}'    # okay for DJGPP compiled

awk "/pattern/ {print \"$1\"}"  # required for Mingw32

Most of my experience comes from version of GNU awk (gawk) compiled for

Win32. Note in particular that DJGPP compilations permit the awk script

to follow Unix quoting syntax '/like/ {"this"}'. However, the user must

know that single quotes under DOS/Windows do not protect the redirection

arrows (<, >) nor do they protect pipes (|). Both are special symbols

for the DOS/CMD command shell and their special meaning is ignored only

if they are placed within "double quotes." Likewise, DOS/Win users must

remember that the percent sign (%) is used to mark DOS/Win environment

variables, so it must be doubled (%%) to yield a single percent sign

visible to awk.

If I am sure that a script will NOT need to be quoted in Unix, DOS, or

CMD, then I normally omit the quote marks. If an example is peculiar to

GNU awk, the command 'gawk' will be used. Please notify me if you find

errors or new commands to add to this list (total length under 65

characters). I usually try to put the shortest script first.

FILE SPACING:

# double space a file

awk '1;{print ""}'

awk 'BEGIN{ORS="\n\n"};1'

# double space a file which already has blank lines in it. Output file

# should contain no more than one blank line between lines of text.

# NOTE: On Unix systems, DOS lines which have only CRLF (\r\n) are

# often treated as non-blank, and thus 'NF' alone will return TRUE.

awk 'NF{print $0 "\n"}'

# triple space a file

awk '1;{print "\n"}'

NUMBERING AND CALCULATIONS:

# precede each line by its line number FOR THAT FILE (left alignment).

# Using a tab (\t) instead of space will preserve margins.

awk '{print FNR "\t" $0}' files*

# precede each line by its line number FOR ALL FILES TOGETHER, with tab.

awk '{print NR "\t" $0}' files*

# number each line of a file (number on left, right-aligned)

# Double the percent signs if typing from the DOS command prompt.

awk '{printf("%5d : %s\n", NR,$0)}'

# number each line of file, but only print numbers if line is not blank

# Remember caveats about Unix treatment of \r (mentioned above)

awk 'NF{$0=++a " :" $0};{print}'

awk '{print (NF? ++a " :" :"") $0}'

# count lines (emulates "wc -l")

awk 'END{print NR}'

# print the sums of the fields of every line

awk '{s=0; for (i=1; i<=NF; i++) s=s+$i; print s}'

# add all fields in all lines and print the sum

awk '{for (i=1; i<=NF; i++) s=s+$i}; END{print s}'

# print every line after replacing each field with its absolute value

awk '{for (i=1; i<=NF; i++) if ($i < 0) $i = -$i; print }'

awk '{for (i=1; i<=NF; i++) $i = ($i < 0) ? -$i : $i; print }'

# print the total number of fields ("words") in all lines

awk '{ total = total + NF }; END {print total}' file

# print the total number of lines that contain "Beth"

awk '/Beth/{n++}; END {print n+0}' file

# print the largest first field and the line that contains it

# Intended for finding the longest string in field #1

awk '$1 > max {max=$1; maxline=$0}; END{ print max, maxline}'

# print the number of fields in each line, followed by the line

awk '{ print NF ":" $0 } '

# print the last field of each line

awk '{ print $NF }'

# print the last field of the last line

awk '{ field = $NF }; END{ print field }'

# print every line with more than 4 fields

awk 'NF > 4'

# print every line where the value of the last field is > 4

awk '$NF > 4'

TEXT CONVERSION AND SUBSTITUTION:

# IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format

awk '{sub(/\r$/,"");print}'   # assumes EACH line ends with Ctrl-M

# IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format

awk '{sub(/$/,"\r");print}

# IN DOS ENVIRONMENT: convert Unix newlines (LF) to DOS format

awk 1

# IN DOS ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format

# Cannot be done with DOS versions of awk, other than gawk:

gawk -v BINMODE="w" '1' infile >outfile

# Use "tr" instead.

tr -d \r outfile            # GNU tr version 1.22 or higher

# delete leading whitespace (spaces, tabs) from front of each line

# aligns all text flush left

awk '{sub(/^[ \t]+/, ""); print}'

# delete trailing whitespace (spaces, tabs) from end of each line

awk '{sub(/[ \t]+$/, "");print}'

# delete BOTH leading and trailing whitespace from each line

awk '{gsub(/^[ \t]+|[ \t]+$/,"");print}'

awk '{$1=$1;print}'           # also removes extra space between fields

# insert 5 blank spaces at beginning of each line (make page offset)

awk '{sub(/^/, "     ");print}'

# align all text flush right on a 79-column width

awk '{printf "%79s\n", $0}' file*

# center all text on a 79-character width

awk '{l=length();s=int((79-l)/2); printf "%"(s+l)"s\n",$0}' file*

# substitute (find and replace) "foo" with "bar" on each line

awk '{sub(/foo/,"bar");print}'           # replaces only 1st instance

gawk '{$0=gensub(/foo/,"bar",4);print}'  # replaces only 4th instance

awk '{gsub(/foo/,"bar");print}'          # replaces ALL instances in a line

# substitute "foo" with "bar" ONLY for lines which contain "baz"

awk '/baz/{gsub(/foo/, "bar")};{print}'

# substitute "foo" with "bar" EXCEPT for lines which contain "baz"

awk '!/baz/{gsub(/foo/, "bar")};{print}'

# change "scarlet" or "ruby" or "puce" to "red"

awk '{gsub(/scarlet|ruby|puce/, "red"); print}'

# reverse order of lines (emulates "tac")

awk '{a[i++]=$0} END {for (j=i-1; j>=0;) print a[j--] }' file*

# if a line ends with a backslash, append the next line to it

# (fails if there are multiple lines ending with backslash...)

awk '/\\$/ {sub(/\\$/,""); getline t; print $0 t; next}; 1' file*

# print and sort the login names of all users

awk -F ":" '{ print $1 | "sort" }' /etc/passwd

# print the first 2 fields, in opposite order, of every line

awk '{print $2, $1}' file

# switch the first 2 fields of every line

awk '{temp = $1; $1 = $2; $2 = temp}' file

# print every line, deleting the second field of that line

awk '{ $2 = ""; print }'

# print in reverse order the fields of every line

awk '{for (i=NF; i>0; i--) printf("%s ",i);printf ("\n")}' file

# remove duplicate, consecutive lines (emulates "uniq")

awk 'a !~ $0; {a=$0}'

# remove duplicate, nonconsecutive lines

awk '! a[$0]++'                     # most concise script

awk '!($0 in a) {a[$0];print}'      # most efficient script

# concatenate every 5 lines of input, using a comma separator

# between fields

awk 'ORS=%NR%5?",":"\n"' file

SELECTIVE PRINTING OF CERTAIN LINES:

# print first 10 lines of file (emulates behavior of "head")

awk 'NR < 11'

# print first line of file (emulates "head -1")

awk 'NR>1{exit};1'

# print the last 2 lines of a file (emulates "tail -2")

awk '{y=x "\n" $0; x=$0};END{print y}'

# print the last line of a file (emulates "tail -1")

awk 'END{print}'

# print only lines which match regular expression (emulates "grep")

awk '/regex/'

# print only lines which do NOT match regex (emulates "grep -v")

awk '!/regex/'

# print the line immediately before a regex, but not the line

# containing the regex

awk '/regex/{print x};{x=$0}'

awk '/regex/{print (x=="" ? "match on line 1" : x)};{x=$0}'

# print the line immediately after a regex, but not the line

# containing the regex

awk '/regex/{getline;print}'

# grep for AAA and BBB and CCC (in any order)

awk '/AAA/; /BBB/; /CCC/'

# grep for AAA and BBB and CCC (in that order)

awk '/AAA.*BBB.*CCC/'

# print only lines of 65 characters or longer

awk 'length > 64'

# print only lines of less than 65 characters

awk 'length < 64'

# print section of file from regular expression to end of file

awk '/regex/,0'

awk '/regex/,EOF'

# print section of file based on line numbers (lines 8-12, inclusive)

awk 'NR==8,NR==12'

# print line number 52

awk 'NR==52'

awk 'NR==52 {print;exit}'          # more efficient on large files

# print section of file between two regular expressions (inclusive)

awk '/Iowa/,/Montana/'             # case sensitive

SELECTIVE DELETION OF CERTAIN LINES:

# delete ALL blank lines from a file (same as "grep '.' ")

awk NF

awk '/./'

CREDITS AND THANKS: