sed

```sample.sh
#!/bin/sh -x
cat file.txt
sed 's/[pz][lz]/xx/' file.txt
```
```
+ cat file.txt
apple
orange
+ sed 's/[pz][lz]/xx/' file.txt
apxxe
orange
```
```
SED(1)                           User Commands                          SED(1)



NAME
       sed - stream editor for filtering and transforming text

SYNOPSIS
       sed [OPTION]... {script-only-if-no-other-script} [input-file]...

DESCRIPTION
       Sed  is a stream editor.  A stream editor is used to perform basic text
       transformations on an input stream (a file or input from  a  pipeline).
       While  in  some  ways similar to an editor which permits scripted edits
       (such as ed), sed works by making only one pass over the input(s),  and
       is consequently more efficient.  But it is sed's ability to filter text
       in a pipeline which particularly distinguishes it from other  types  of
       editors.

       -n, --quiet, --silent

              suppress automatic printing of pattern space

       -e script, --expression=script

              add the script to the commands to be executed

       -f script-file, --file=script-file

              add the contents of script-file to the commands to be executed

       --follow-symlinks

              follow symlinks when processing in place

       -i[SUFFIX], --in-place[=SUFFIX]

              edit files in place (makes backup if SUFFIX supplied)

       -c, --copy

              use copy instead of rename when shuffling files in -i mode

       -b, --binary

              does  nothing;  for  compatibility with WIN32/CYGWIN/MSDOS/EMX (
              open files in binary mode (CR+LFs are not treated specially))

       -l N, --line-length=N

              specify the desired line-wrap length for the `l' command

       --posix

              disable all GNU extensions.

       -r, --regexp-extended

              use extended regular expressions in the script.

       -s, --separate

              consider files as separate rather than as  a  single  continuous
              long stream.

       -u, --unbuffered

              load  minimal amounts of data from the input files and flush the
              output buffers more often

       -z, --null-data

              separate lines by NUL characters

       --help

              display this help and exit

       --version

              output version information and exit

       If no -e, --expression, -f, or --file option is given, then  the  first
       non-option  argument  is  taken  as  the  sed script to interpret.  All
       remaining arguments are names of input files; if  no  input  files  are
       specified, then the standard input is read.

       GNU  sed  home  page: <http://www.gnu.org/software/sed/>.  General help
       using GNU software: <http://www.gnu.org/gethelp/>.  E-mail bug  reports
       to:  <bug-sed@gnu.org>.   Be sure to include the word ``sed'' somewhere
       in the ``Subject:'' field.

COMMAND SYNOPSIS
       This is just a brief synopsis of sed commands to serve as a reminder to
       those  who  already  know sed; other documentation (such as the texinfo
       document) must be consulted for fuller descriptions.

   Zero-address ``commands''
       : label
              Label for b and t commands.

       #comment
              The comment extends until the next newline (or the end of  a  -e
              script fragment).

       }      The closing bracket of a { } block.

   Zero- or One- address commands
       =      Print the current line number.

       a \

       text   Append text, which has each embedded newline preceded by a back‐
              slash.

       i \

       text   Insert text, which has each embedded newline preceded by a back‐
              slash.

       q [exit-code]
              Immediately  quit  the  sed  script  without processing any more
              input, except that if auto-print is  not  disabled  the  current
              pattern  space will be printed.  The exit code argument is a GNU
              extension.

       Q [exit-code]
              Immediately quit the sed  script  without  processing  any  more
              input.  This is a GNU extension.

       r filename
              Append text read from filename.

       R filename
              Append  a  line read from filename.  Each invocation of the com‐
              mand reads a line from the file.  This is a GNU extension.

   Commands which accept address ranges
       {      Begin a block of commands (end with a }).

       b label
              Branch to label; if label is omitted, branch to end of script.

       c \

       text   Replace the selected lines with text, which  has  each  embedded
              newline preceded by a backslash.

       d      Delete pattern space.  Start next cycle.

       D      If  pattern  space contains no newline, start a normal new cycle
              as if the d command was issued.  Otherwise, delete text  in  the
              pattern  space  up  to the first newline, and restart cycle with
              the resultant pattern space,  without  reading  a  new  line  of
              input.

       h H    Copy/append pattern space to hold space.

       g G    Copy/append hold space to pattern space.

       l      List out the current line in a ``visually unambiguous'' form.

       l width
              List  out  the  current line in a ``visually unambiguous'' form,
              breaking it at width characters.  This is a GNU extension.

       n N    Read/append the next line of input into the pattern space.

       p      Print the current pattern space.

       P      Print up to the first embedded newline of  the  current  pattern
              space.

       s/regexp/replacement/
              Attempt  to match regexp against the pattern space.  If success‐
              ful,  replace  that  portion  matched  with  replacement.    The
              replacement may contain the special character & to refer to that
              portion of the pattern space  which  matched,  and  the  special
              escapes  \1  through  \9  to refer to the corresponding matching
              sub-expressions in the regexp.

       t label
              If a s/// has done a  successful  substitution  since  the  last
              input  line  was  read  and  since the last t or T command, then
              branch to label; if label is omitted, branch to end of script.

       T label
              If no s/// has done a successful  substitution  since  the  last
              input  line  was  read  and  since the last t or T command, then
              branch to label; if label is omitted, branch to end  of  script.
              This is a GNU extension.

       w filename
              Write the current pattern space to filename.

       W filename
              Write  the  first line of the current pattern space to filename.
              This is a GNU extension.

       x      Exchange the contents of the hold and pattern spaces.

       y/source/dest/
              Transliterate the characters in the pattern space  which  appear
              in source to the corresponding character in dest.

Addresses
       Sed  commands can be given with no addresses, in which case the command
       will be executed for all input lines; with one address, in  which  case
       the  command  will  only  be  executed for input lines which match that
       address; or with two addresses, in which case the command will be  exe‐
       cuted  for  all  input  lines  which match the inclusive range of lines
       starting from the first address and continuing to the  second  address.
       Three  things  to  note about address ranges: the syntax is addr1,addr2
       (i.e., the addresses are separated by a comma); the  line  which  addr1
       matched will always be accepted, even if addr2 selects an earlier line;
       and if addr2 is a regexp, it will not be tested against the  line  that
       addr1 matched.

       After  the address (or address-range), and before the command, a !  may
       be inserted, which specifies that the command shall only be executed if
       the address (or address-range) does not match.

       The following address types are supported:

       number Match  only  the specified line number (which increments cumula‐
              tively across files, unless the -s option is  specified  on  the
              command line).

       first~step
              Match every step'th line starting with line first.  For example,
              ``sed -n 1~2p'' will print all the  odd-numbered  lines  in  the
              input  stream,  and the address 2~5 will match every fifth line,
              starting with the second.  first can be zero; in this case,  sed
              operates as if it were equal to step.  (This is an extension.)

       $      Match the last line.

       /regexp/
              Match lines matching the regular expression regexp.

       \cregexpc
              Match  lines  matching the regular expression regexp.  The c may
              be any character.

       GNU sed also supports some special 2-address forms:

       0,addr2
              Start out in "matched  first  address"  state,  until  addr2  is
              found.  This is similar to 1,addr2, except that if addr2 matches
              the very first line of input the 0,addr2 form will be at the end
              of  its  range,  whereas  the  1,addr2 form will still be at the
              beginning of its range.  This works only when addr2 is a regular
              expression.

       addr1,+N
              Will match addr1 and the N lines following addr1.

       addr1,~N
              Will  match  addr1  and the lines following addr1 until the next
              line whose input line number is a multiple of N.

REGULAR EXPRESSIONS
       POSIX.2 BREs should be supported, but they aren't completely because of
       performance  problems.  The \n sequence in a regular expression matches
       the newline character, and similarly for \a, \t, and other sequences.

BUGS
       E-mail bug reports to bug-sed@gnu.org.  Also, please include the output
       of ``sed --version'' in the body of your report if at all possible.

AUTHOR
       Written by Jay Fenlason, Tom Lord, Ken Pizzini, and Paolo Bonzini.  GNU
       sed home page: <http://www.gnu.org/software/sed/>.  General help  using
       GNU  software:  <http://www.gnu.org/gethelp/>.   E-mail bug reports to:
       <bug-sed@gnu.org>.  Be sure to include the word  ``sed''  somewhere  in
       the ``Subject:'' field.

COPYRIGHT
       Copyright  ©  2012  Free Software Foundation, Inc.  License GPLv3+: GNU
       GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free  to  change  and  redistribute  it.
       There is NO WARRANTY, to the extent permitted by law.

SEE ALSO
       awk(1),  ed(1),  grep(1),  tr(1),  perlre(1),  sed.info, any of various
       books on sed, the sed FAQ (http://sed.sf.net/grabbag/tutorials/sed‐
       faq.txt), http://sed.sf.net/grabbag/.

       The full documentation for sed is maintained as a Texinfo manual.  If
       the info and sed programs are properly installed at your site, the com‐
       mand

              info sed

       should give you access to the complete manual.



sed 4.2.2                       September 2020                          SED(1)
```