Why is sed not recognizing t as a tab

Question

sed  s         t 1    filename  gt   sedTmpFile  amp  amp  mv  sedTmpFile  filename   I am expecting this sed script to insert a tab in front of every line in  filename however it is not  For some reason it is inserting a t instead

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I used this on Mac   sed -i       i   n   thello n  filename   Used this link for reference

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Using Bash you may insert a TAB character programmatically like so   TAB    t   echo  line    sed  s      TAB  amp  g   echo  line    sed  s        TAB    amp  g      use of Bash string concatenation

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Use   echo   t    You ll need quotes around the pattern   Eg  To remove a tab   sed  s   echo   t

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Not all versions of sed understand  t  Just insert a literal tab instead  press Ctrl-V then Tab

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I ve used something like this with a Bash shell on Ubuntu 12 04  LTS    To append a new line with tab second when first is matched   sed -i   first a   t second  filename   To replace first with tab second   sed -i  s first   t second g  filename

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sedit was on the right path  but it s a bit awkward to define a variable   Solution  bash specific   The way to do this in bash is to put a dollar sign in front of your single quoted string     echo -e  1 n2 n3  1 2 3    echo -e  1 n2 n3    sed  s     t amp  g  t1 t2 t3    echo -e  1 n2 n3    sed   s     t amp  g      1     2     3   If your string needs to include variable expansion  you can put quoted strings together like so     timestamp   date   s    echo -e  1 n2 n3    sed  s     timestamp    t amp  g  1491237958  1 1491237958  2 1491237958  3   Explanation  In bash   string  causes  ANSI-C expansion   And that is what most of us expect when we use things like  t   r   n  etc  From  https   www gnu org software bash manual html node ANSI 002dC-Quoting html ANSI 002dC-Quoting     Words of the form   string  are treated specially  The word expands   to string  with backslash-escaped characters replaced as specified by   the ANSI C standard  Backslash escape sequences  if present  are   decoded         The expanded result is single-quoted  as if the dollar sign had not   been present    Solution  if you must avoid bash   I personally think most efforts to avoid bash are silly because avoiding bashisms does NOT  make your code portable   Your code will be less brittle if you shebang it to bash -eu than if you try to avoid bash and use sh  unless you are an absolute POSIX ninja    But rather than have a religious argument about that  I ll just give you the BEST  answer     echo -e  1 n2 n3    sed  s      printf   t   amp  g      1     2     3     BEST answer  Yes  because one example of what most anti-bash shell scripters would do wrong in their code is use echo   t  as in  robrecord s answer  That will work for GNU echo  but not BSD echo  That is explained by The Open Group at http   pubs opengroup org onlinepubs 9699919799 utilities echo html tag 20 37 16 And this is an example of why trying to avoid bashisms usually fail

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If you know that certain characters are not used  you can translate  quot  t quot  into something else  cat my file   tr  quot  t quot   quot   quot    sed  quot s        1  quot

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You don t need to use sed to do a substitution when in actual fact  you just want to insert a tab in front of the line  Substitution for this case is an expensive operation as compared to just printing it out  especially when you are working with big files  Its easier to read too as its not regex   eg using awk  awk   print   t  0    filename  gt  temp  amp  amp  mv temp  filename

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TAB   printf   t   sed  quot s   TAB   g quot  input file  It works for me on Red Hat  which will remove tabs from the input file

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Instead of BSD sed  i use perl   ct MBA45    python -c  print   t t thi     perl -0777pe  s  t   g     hi

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I think others have clarified this adequately for other approaches  sed  AWK  etc    However  my bash-specific answers  tested on macOS High Sierra and CentOS 6 7  follow    1  If OP wanted to use a search-and-replace method similar to what they originally proposed  then I would suggest using perl for this  as follows  Notes  backslashes before parentheses for regex shouldn t be necessary  and this code line reflects how  1 is better to use than  1 with perl substitution operator  e g  per Perl 5 documentation    perl -pe  s       t 1    filename  gt   sedTmpFile  amp  amp  mv  sedTmpFile  filename   2  However  as pointed out by ghostdog74  since the desired operation is actually to simply add a tab at the start of each line before changing the tmp file to the input target file   filename   I would recommend perl again but with the following modification s    perl -pe  s    t    filename  gt   sedTmpFile  amp  amp  mv  sedTmpFile  filename    OR perl -pe   s    t    filename  gt   sedTmpFile  amp  amp  mv  sedTmpFile  filename   3  Of course  the tmp file is superfluous  so it s better to just do everything  in place   adding -i flag  and simplify things to a more elegant one-liner with  perl -i -pe   s    t    filename

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sed doesn t support  t  nor other escape sequences like  n for that matter  The only way I ve found to do it was to actually insert the tab character in the script using sed   That said  you may want to consider using Perl or Python  Here s a short Python script I wrote that I use for all stream regex ing      usr bin env python import sys import re  def main args     if len args   lt  2      print  gt  gt  sys stderr   Usage   lt search-pattern gt   lt replace-expr gt       raise SystemExit    p   re compile args 0   re MULTILINE   re DOTALL    s   sys stdin read     print p sub args 1   s    if   name         main       main sys argv 1

[regex] Why is sed not recognizing \t as a tab?

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