AWK

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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};1'
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'
# print the last X fields
# if you have e.g. a filename test.file.tar.gz
awk -F. '{s=NF-1; print $s" "$NF}'

Random number generation

# generate a pseudo-random seed
SEED=`head -1 /dev/urandom | od -N 1 | head -1 | awk '{ print $2 }'`

# paranoid!! ;-)
# not really needed...
let SEED=$SEED*$$

# use this seed to initialize rand()-function of awk
# and print out NON-negative integers with a maximum value of 15
echo | awk " { srand($SEED); print int(15 * rand()) } "

STRING CREATION

# create a string of a specific length (e.g., generate 513 spaces)
awk 'BEGIN{while (a++<513) s=s " "; print s}'
# insert a string of specific length at a certain character position
# Example: insert 49 spaces after column #6 of each input line.
gawk --re-interval 'BEGIN{while(a++<49)s=s " "};{sub(/^.{6}/,"&" s)};1'


FORMATED OUTPUT (Space padding)

do create some formated output of lines/fields

awk '{X=50-length($3); printf "%s", $3; printf "%*s", X, " "; print "--> "$4}'


ARRAY CREATION

# These next 2 entries are not one-line scripts, but the technique
# is so handy that it merits inclusion here.

# create an array named "month", indexed by numbers, so that month[1]
# is 'Jan', month[2] is 'Feb', month[3] is 'Mar' and so on.
split("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec", month, " ")
# create an array named "mdigit", indexed by strings, so that
# mdigit["Jan"] is 1, mdigit["Feb"] is 2, etc. Requires "month" array
for (i=1; i<=12; i++) mdigit[month[i]] = i

TEXT CONVERSION AND SUBSTITUTION

# IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format
awk '{sub(/\r$/,"")};1'   # assumes EACH line ends with Ctrl-M
# IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format
awk '{sub(/$/,"\r")};1'
# 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 <infile >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]+/, "")};1'
# delete trailing whitespace (spaces, tabs) from end of each line
awk '{sub(/[ \t]+$/, "")};1'
# delete BOTH leading and trailing whitespace from each line
awk '{gsub(/^[ \t]+|[ \t]+$/,"")};1'
awk '{$1=$1};1'           # also removes extra space between fields
# insert 5 blank spaces at beginning of each line (make page offset)
awk '{sub(/^/, "     ")};1'
# 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")}; 1'           # replace only 1st instance
gawk '{$0=gensub(/foo/,"bar",4)}; 1'  # replace only 4th instance
awk '{gsub(/foo/,"bar")}; 1'          # replace ALL instances in a line
# substitute "foo" with "bar" ONLY for lines which contain "baz"
awk '/baz/{gsub(/foo/, "bar")}; 1'
# substitute "foo" with "bar" EXCEPT for lines which contain "baz"
awk '!/baz/{gsub(/foo/, "bar")}; 1'
# change "scarlet" or "ruby" or "puce" to "red"
awk '{gsub(/scarlet|ruby|puce/, "red")}; 1'
# 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);print ""}' file
# concatenate every 5 lines of input, using a comma separator
# between fields
awk 'ORS=NR%5?",":"\n"' file
# substitute " in special fields here: last field in the line
# or ; in e.g. second field 
awk '{gsub("\"","", $NF); print $NF}'
awk '{gsub(";","", $2); print $2}'

REGEX BACKREFERENCING

echo "Paul loves Mary" | gawk '{print gensub(/(.*) (.*) (.*)/,"\\3 \\2 \\1","")}'
Mary loves Paul

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 any line where field #5 is equal to "abc123"
awk '$5 == "abc123"'
# print only those lines where field #5 is NOT equal to "abc123"
# This will also print lines which have less than 5 fields.
awk '$5 != "abc123"'
awk '!($5 == "abc123")'
# matching a field against a regular expression
awk '$7  ~ /^[a-f]/'    # print line if field #7 matches regex
awk '$7 !~ /^[a-f]/'    # print line if field #7 does NOT match regex
# print the line immediately before a regex, but not the line
# containing the regex
awk '/regex/{print x};{x=$0}'
awk '/regex/{print (NR==1 ? "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 on the same line)
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
# Gibt den Inhalt eines Files zwischen zwei
# Regex aus. (Inclusive der Regex). Die Abfrage
# ist case sensitiv
awk '/Iowa/,/Montana/'

SELECTIVE DELETION OF CERTAIN LINES

# delete ALL blank lines from a file (same as "grep '.' ")
awk NF
awk '/./'
# 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
# delete a line that matches PATTERN
# and additionaly the following 2 lines
# modify c=3 to delete more/less lines
awk '/PATTERN-To-Be-Deleted/{c=3} c&&c--{next} 1'

Snippets

Alle remote-user auf dem lokalen system killen

w | awk '$3 !~ /:0(\.0)?|-/ && $2 ~ /pts/ {print "/dev/"$2}' | xargs fuser -k

oder

w -h | awk '$3 !~ /:0(\.0)?|-/ {print "/dev/"$2} | xargs fuser -k'

in regelmaessigen abstaenden einfach in 'watch' oder in 'while true' verpacken erklaerung zum awk-command:

  1. matched in feld 3 auf :0 UND :0.0 oder auf -
  2. und matched feld 2 auf pts (nur noetig wenn 'w' benutzt wird NICHT bei 'w -h' schadet aber auch nicht!! ;-))
  3. trifft beides zu wird das devicefile ausgegeben

mit fuser wird der user dann gekickt... oder was immer man mit dem user tun will! ;-)