How to replace multiple patterns at once with sed

Question

Suppose I have  abbc  string and I want to replace    ab -  bc bc -  ab   If I try two replaces the result is not what I want   echo  abbc    sed  s ab bc g s bc ab g  abab   So what sed command can I use to replace like below   echo abbc   sed SED COMMAND bcab   EDIT  Actually the text could have more than 2 patterns and I don t know how many replaces I will need  Since there was a answer saying that sed is a stream editor and its replaces are greedily I think that I will need to use some script language for that

User · Answer

I believe this should solve your problem. I may be missing a few edge cases, please comment if you notice one.

You need a way to exclude previous substitutions from future patterns, which really means making outputs distinguishable, as well as excluding these outputs from your searches, and finally making outputs indistinguishable again. This is very similar to the quoting/escaping process, so I'll draw from it.

s/\\/\\\\/g escapes all existing backslashes
s/ab/\\b\\c/g substitutes raw ab for escaped bc
s/bc/\\a\\b/g substitutes raw bc for escaped ab
s/\\\(.\)/\1/g substitutes all escaped X for raw X

I have not accounted for backslashes in ab or bc, but intuitively, I would escape the search and replace terms the same way - \ now matches \\, and substituted \\ will appear as \.

Until now I have been using backslashes as the escape character, but it's not necessarily the best choice. Almost any character should work, but be careful with the characters that need escaping in your environment, sed, etc. depending on how you intend to use the results.

User · Answer

I always use multiple statements with  -e     sed -e  s AND  n amp  g  -e  s GROUP BY  n amp  g  -e  s UNION  n amp  g  -e  s FROM  n amp  g  file  gt  readable sql  This will append a   n  before all AND s  GROUP BY s  UNION s and FROM s  whereas   amp   means the matched string and   n amp   means you want to replace the matched string with an   n  before the  matched

User · Answer

sed is a stream editor  It searches and replaces greedily  The only way to do what you asked for is using an intermediate substitution pattern and changing it back in the end   echo  abcd    sed -e  s ab xy  s cd ab  s xy cd

User · Answer

echo   quot C  Users San Tan My Folder project1 quot    sed -e  s C    mnt  c    s       g  replaces C  Users San Tan My Folder project1 to mnt c Users San Tan My Folder project1 in case someone needs to replace windows paths to Windows Subsystem for Linux WSL  paths

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If replacing the string by Variable  the solution doesn t work  The sed command need to be in double quotes instead on single quote   sed -e  quot s  replacevarServiceName   varServiceName g quot  -e  quot s  replacevarImageTag   varImageTag g quot  deployment yaml

User · Answer

Tcl has a builtin for this    tclsh   string map  ab bc bc ab  abbc bcab   This works by walking the string a character at a time doing string comparisons starting at the current position    In perl   perl -E       sub string map           my   str   map                my  i   0          while   i  lt  length  str              KEYS              for my  key  keys  map                    if  substr  str   i  length  key  eq  key                        substr  str   i  length  key     map  key                        i    length  map  key   - 1                      last KEYS                                               i                      return  str            say string map  abbc    ab   gt  bc    bc   gt  ab          bcab

User · Answer

This might work for you  GNU sed    sed -r  1 x s    abbc bcab  x  G s    n   a   n n  P d  s  n ab bc     n     1           4 n 2  ta s  n     1 n  ta  file   This uses a lookup table which is prepared and held in the hold space  HS  and then appended to each line  An unique marker  in this case  n  is prepended to the start of the line and used as a method to bump-along the search throughout the length of the line  Once the marker reaches the end of the line the process is finished and is printed out the lookup table and markers being discarded   N B  The lookup table is prepped at the very start and a second unique marker  in this case    chosen so as not to clash with the substitution strings   With some comments   sed -r       initialize hold with  abbc bcab   1       x     s    abbc bcab      x        G          append hold to patt  after a  n     s    n     prepend a  n     a      n n        P        print patt up to first  n     d        delete patt  amp  start next cycle        s  n ab bc     n     1           4 n 2    ta         goto a if sub occurred    s  n     1 n     move one char past the first  n   ta         goto a if sub occurred     The table works like this                replacement  abbc bcab              pattern

User · Answer

Here is a variation on ooga s answer that works for multiple search and replace pairs without having to check how values might be reused   sed -i   s  bAB b         BC         g s  bBC b         CD         g s           g   path to your files   txt   Here is an example   before   some text AB some more text  BC  and more text    after   some text BC some more text  CD  and more text    Note that  b denotes word boundaries  which is what prevents the          from interfering with the search  I m using GNU sed 4 2 2 on Ubuntu    If you are not using a word boundary search  then this technique may not work   Also note that this gives the same results as removing the s           g and appending  amp  amp  sed -i  s           g  path to your files   txt to the end of the command  but doesn t require specifying the path twice   A general variation on this would be to use  x0 or   x0  in place of          if you know that no nulls appear in your files  as jthill suggested

User · Answer

Maybe something like this   sed  s ab    g  s bc ab g  s    bc g    Replace   with a character that you know won t be in the string

User · Answer

Here is an awk based on oogas sed  echo  abbc    awk   gsub  ab   xy   gsub  bc   ab   gsub  xy   bc   1  bcab

User · Answer

May be a simpler approach for single pattern occurrence you can try as below    echo  abbc    sed  s ab bc  s bc ab 2   My output       echo  abbc    sed  s ab bc  s bc ab 2   bcab   For multiple occurrences of pattern   sed  s   ab    bc    2 1 g    Example     cat try txt abbc abbc abbc bcab abbc bcab abbc abbc bcab     sed  s   ab    bc    2 1 g  try txt bcab bcab bcab bcab bcab bcab bcab bcab bcab   Hope this helps

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