有趣的awkline

碰到一些有趣的awk line command

 awk '1;{print ""}'

 awk 'BEGIN{ORS="\n\n"};1'

 awk 'NF{print $0 "\n"}'

 awk '1;{print "\n"}'

 awk '{print FNR "\t" $0}' files*

 awk '{print NR "\t" $0}' files*

 awk '{printf("%5d : %s\n", NR,$0)}'

 awk 'NF{$0=++a " :" $0};1'

 awk '{print (NF? ++a " :" :"") $0}'

 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'

 # 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'

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

 # 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

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

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