How can I repeat a character in Bash

Question

How could I do this with echo   perl -E  say     x 100

User · Answer

In case that you want to repeat a character n times being n a VARIABLE number of times depending on, say, the length of a string you can do:

#!/bin/bash
vari='AB'
n=$(expr 10 - length $vari)
echo 'vari equals.............................: '$vari
echo 'Up to 10 positions I must fill with.....: '$n' equal signs'
echo $vari$(perl -E 'say "=" x '$n)

It displays:

vari equals.............................: AB  
Up to 10 positions I must fill with.....: 8 equal signs  
AB========

User · Answer

You can use   printf     0s   1  100    How this works   Bash expands  1  100  so the command becomes   printf     0s  1 2 3 4     100   I ve set printf s format to    0s which means that it will always print a single   no matter what argument it is given  Therefore it prints 100  s

User · Answer

A more elegant alternative to the proposed Python solution could be   python -c  print      1000

User · Answer

If you want POSIX-compliance and consistency across different implementations of echo and printf  and or shells other than just bash   seq    n  1  while    n -le  2    do echo  n  n    n 1    done      If you don t have it   echo   for each in   seq 1 100   do printf      done       will produce the same output as perl -E  say     x 100  just about everywhere

User · Answer

My proposal  accepting variable values for n    n 100 seq 1  n   xargs -I    printf

User · Answer

The question was about how to do it with echo   echo -e      1  100   b     This will will do exactly the same as perl -E  say     x 100  but with echo only

User · Answer

My answer is a bit more complicated  and probably not perfect  but for those looking to output large numbers  I was able to do around 10 million in 3 seconds   repeatString          argument 1  The string to print       argument 2  The number of times to print     stringToPrint  1     length  2        Find the largest integer value of x in 2 x  number of times to repeat  using logarithms     power  echo  l   length   l 2     bc -l      power  echo  scale 0    power  1    bc         Get the difference between the length and 2 x     diff  echo    length  - 2   power     bc         Double the string length to the power of x     for i in  seq    power     do          stringToPrint    stringToPrint   stringToPrint       done       Since we know that the string is now at least bigger than half the total  grab however many more we need and add it to the string      stringToPrint    stringToPrint   stringToPrint 0   diff        echo   stringToPrint

User · Answer

As others have said  in bash brace expansion precedes parameter expansion  so  m n  ranges can only contain literals  seq and jot provide clean solutions but aren t fully portable from one system to another  even if you re using the same shell on each   Though seq is increasingly available  e g   in FreeBSD 9 3 and higher   eval and other forms of indirection always work but are somewhat inelegant   Fortunately  bash supports C-style for loops  with arithmetic expressions only   So here s a concise  pure bash  way   repecho     for   i 0  i lt  1    i    do echo -n   2   done  echo      This takes the number of repetitions as the first argument and the string to be repeated  which may be a single character  as in the problem description  as the second argument  repecho 7 b outputs bbbbbbb  terminated by a newline    Dennis Williamson gave essentially this solution four years ago in his excellent answer to Creating string of repeated characters in shell script  My function body differs slightly from the code there    Since the focus here is on repeating a single character and the shell is bash  it s probably safe to use echo instead of printf  And I read the problem description in this question as expressing a preference to print with echo  The above function definition works in bash and ksh93  Although printf is more portable  and should usually be used for this sort of thing   echo s syntax is arguably more readable   Some shells  echo builtins interpret - by itself as an option--even though the usual meaning of -  to use stdin for input  is nonsensical for echo  zsh does this  And there definitely exist echos that don t recognize -n  as it is not standard   Many Bourne-style shells don t accept C-style for loops at all  thus their echo behavior needn t be considered    Here the task is to print the sequence  there  it was to assign it to a variable    If  n is the desired number of repetitions and you don t have to reuse it  and you want something even shorter   while   n--    do echo -n   s   done  echo   n must be a variable--this way doesn t work with positional parameters   s is the text to be repeated

User · Answer

function repeatString         local -r string    1       local -r numberToRepeat    2        if       string          amp  amp     numberToRepeat        1-9  0-9           then         local -r result    printf     numberToRepeat s            echo -e    result      string        fi     Sample runs    repeatString  a1  10  a1a1a1a1a1a1a1a1a1a1    repeatString  a1  0     repeatString    10    Reference lib at  https   github com gdbtek linux-cookbooks blob master libraries util bash

User · Answer

This is the longer version of what Eliah Kagan was espousing   while       i--    -gt 0    do echo -n       done   Of course you can use printf for that as well  but not really to my liking   printf       i 2   s    This version is Dash compatible   until       i i-1    -lt 0    do echo -n       done   with i being the initial number

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Tip of the hat to  gniourf gniourf for his input   Note  This answer does not answer the original question  but complements the existing  helpful answers by comparing performance   Solutions are compared in terms of execution speed only - memory requirements are not taken into account  they vary across solutions and may matter with large repeat counts    Summary    If your repeat count is small  say up to around 100  it s worth going with the Bash-only solutions  as the startup cost of external utilities matters  especially Perl s    Pragmatically speaking  however  if you only  need one instance of repeating characters  all existing solutions may be fine   With large repeat counts  use external utilities  as they ll be much faster    In particular  avoid Bash s global substring replacement with large strings  e g     var         as it is prohibitively slow     The following are timings taken on a late-2012 iMac with a 3 2 GHz Intel Core i5 CPU and a Fusion Drive  running OSX 10 10 4 and bash 3 2 57  and are the average of 1000 runs   The entries are    listed in ascending order of execution duration  fastest first  prefixed with    M     a potentially multi-character solution S     a single-character-only solution P     a POSIX-compliant solution  followed by a brief description of the solution suffixed with the name of the author of the originating answer      Small repeat count  100    M  P  printf   s   dogbane                             0 0002  M     printf   bash global substr  replacement  Tim    0 0005  M     echo -n - brace expansion loop  eugene y         0 0007  M     echo -n - arithmetic loop  Eliah Kagan           0 0013  M     seq -f  Sam Salisbury                            0 0016  M     jot -b  Stefan Ludwig                            0 0016  M     awk -   count 1       Steven Penny  variant      0 0019  M  P  awk - while loop  Steven Penny                   0 0019  S     printf   tr  user332325                          0 0021  S     head   tr  eugene y                              0 0021  S  P  dd   tr  mklement0                               0 0021  M     printf   sed  user332325  comment                0 0021  M     mawk -   count 1       Steven Penny  variant     0 0025  M  P  mawk - while loop  Steven Penny                  0 0026  M     gawk -   count 1       Steven Penny  variant     0 0028  M  P  gawk - while loop  Steven Penny                  0 0028  M     yes   head   tr  Digital Trauma                  0 0029  M     Perl  sid com                                    0 0059    The Bash-only solutions lead the pack - but only with a repeat count this small   see below   Startup cost of external utilities does matter here  especially Perl s  If you must call this in a loop - with small repetition counts in each iteration - avoid the multi-utility  awk  and perl solutions       Large repeat count  1000000  1 million     M     Perl  sid com                                    0 0067  M     mawk -   count 1       Steven Penny  variant     0 0254  M     gawk -   count 1       Steven Penny  variant     0 0599  S     head   tr  eugene y                              0 1143  S  P  dd   tr  mklement0                               0 1144  S     printf   tr  user332325                          0 1164  M  P  mawk - while loop  Steven Penny                  0 1434  M     seq -f  Sam Salisbury                            0 1452  M     jot -b  Stefan Ludwig                            0 1690  M     printf   sed  user332325  comment                0 1735  M     yes   head   tr  Digital Trauma                  0 1883  M  P  gawk - while loop  Steven Penny                  0 2493  M     awk -   count 1       Steven Penny  variant      0 2614  M  P  awk - while loop  Steven Penny                   0 3211  M  P  printf   s   dogbane                             2 4565  M     echo -n - brace expansion loop  eugene y         7 5877  M     echo -n - arithmetic loop  Eliah Kagan           13 5426  M     printf   bash global substr  replacement  Tim    n a    The Perl solution from the question is by far the fastest  Bash s global string-replacement    foo        is inexplicably excruciatingly slow with large strings  and has been taken out of the running  took around 50 minutes    in Bash 4 3 30  and even longer in Bash 3 2 57 - I never waited for it to finish   Bash loops are slow  and arithmetic loops     i  0          are slower than brace-expanded ones   1  n   - though arithmetic loops are more memory-efficient  awk refers to BSD awk  as also found on OSX  - it s noticeably slower than gawk  GNU Awk  and especially mawk  Note that with large counts and multi-char  strings  memory consumption can become a consideration - the approaches differ in that respect      Here s the Bash script  testrepeat  that produced the above  It takes 2 arguments    the character repeat count optionally  the number of test runs to perform and to calculate the average timing from   In other words  the timings above were obtained with testrepeat 100 1000 and testrepeat 1000000 1000     usr bin env bash  title     printf   s  t    1      TIMEFORMAT    6Rs     The number of repetitions of the input chars  to produce COUNT REPETITIONS   1 Arguments   lt charRepeatCount gt    lt testRunCount gt       The number of test runs to perform to derive the average timing from  COUNT RUNS   2 -1     Discard the  stdout  output generated by default    If you want to check the results  replace   dev null  on the following   line with a prefix path to which a running index starting with 1 will   be appended for each test run  e g   outFilePrefix  outfile   which   will produce outfile1  outfile2      outFilePrefix  dev null       outFile  outFilePrefix   ndx 0    title   M  P  printf   s   dogbane         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx           In order to use brace expansion with a variable  we must use  eval     eval     time for    n   0  n  lt  COUNT RUNS  n       do      printf    s    1   COUNT REPETITIONS   gt   outFile    done     title   M     echo -n - arithmetic loop  Eliah Kagan         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      for   i 0  i lt COUNT REPETITIONS    i    do echo -n    done  gt   outFile    done     title   M     echo -n - brace expansion loop  eugene y         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx           In order to use brace expansion with a variable  we must use  eval     eval     time for    n   0  n  lt  COUNT RUNS  n       do      for i in  1   COUNT REPETITIONS   do echo -n    done  gt   outFile    done        title   M     printf   sed  user332325  comment          outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      printf     COUNT REPETITIONS s    sed  s     g   gt   outFile    done     title   S     printf   tr  user332325         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      printf     COUNT REPETITIONS s    tr           gt   outFile    done     title   S     head   tr  eugene y         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      head -c  COUNT REPETITIONS  lt   dev zero   tr   0       gt   outFile    done     title   M     seq -f  Sam Salisbury         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      seq -f     -s     COUNT REPETITIONS  gt   outFile    done     title   M     jot -b  Stefan Ludwig         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      jot -s    -b      COUNT REPETITIONS  gt   outFile    done     title   M     yes   head   tr  Digital Trauma         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      yes     head - COUNT REPETITIONS   tr -d   n    gt   outFile    done    title   M     Perl  sid com         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      perl -e  print       x  COUNT REPETITIONS   gt   outFile    done    title   S  P  dd   tr  mklement0         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx      time for    n   0  n  lt  COUNT RUNS  n       do      dd if  dev zero bs  COUNT REPETITIONS count 1 2 gt  dev null   tr   0       gt   outFile    done         On OSX  awk is BSD awk  and mawk and gawk were installed later         On Linux systems  awk may refer to either mawk or gawk    for awkBin in awk mawk gawk  do     if    -x   command -v  awkBin      then        title   M      awkBin   -   count 1       Steven Penny  variant              outFile      dev null      amp  amp  outFile   outFilePrefix     ndx          time for    n   0  n  lt  COUNT RUNS  n       do           awkBin -v count  COUNT REPETITIONS  BEGIN   OFS        count 1      print     gt   outFile        done        title   M  P   awkBin   - while loop  Steven Penny             outFile      dev null      amp  amp  outFile   outFilePrefix     ndx          time for    n   0  n  lt  COUNT RUNS  n       do           awkBin -v count  COUNT REPETITIONS  BEGIN   while  i    lt  count  printf         gt   outFile        done      fi   done    title   M     printf   bash global substr  replacement  Tim         outFile      dev null      amp  amp  outFile   outFilePrefix     ndx           In Bash 4 3 30 a single run with repeat count of 1 million took almost        50  minutes     to complete  n Bash 3 2 57 it s seemingly even slower -        didn t wait for it to finish         Thus  this test is skipped for counts that are likely to be much slower        than the other tests    skip 0       BASH VERSINFO -le 3  amp  amp  COUNT REPETITIONS -gt 1000     amp  amp  skip 1       BASH VERSINFO -eq 4  amp  amp  COUNT REPETITIONS -gt 10000     amp  amp  skip 1   if    skip     then     echo  n a   gt  amp 2   else     time for    n   0  n  lt  COUNT RUNS  n       do          printf -v t     COUNT REPETITIONS s       printf  s    t            gt   outFile      done   fi   2 gt  amp 1     sort -t   t  -k2 2n       awk -F    t  -v count  COUNT RUNS         printf   s t    1       if   2     n a     print  2   else   printf    4f n    2   count            column -s   t  -t

User · Answer

How could I do this with echo    You can do this with echo if the echo is followed by sed   echo   sed -r   a s          1       100   q  ba    Actually  that echo is unnecessary there

User · Answer

Another option is to use GNU seq and remove all numbers and newlines it generates   seq -f    0f  100   tr -d   n0123456789    This command prints the   character 100 times

User · Answer

There is no simple way  Avoid loops using printf and substitution   str   printf   40s   echo   str    rep    echoes  rep  40 times

User · Answer

repeat            1 number of patterns to repeat        2 pattern     printf -v  TEMP     s    1      echo   TEMP     2

User · Answer

Here s two interesting ways    ubuntu ubuntu    yes     head -10   paste -s -d    -            ubuntu ubuntu    yes     head -10   tr -d   n            ubuntu ubuntu       Note these two are subtly different - The paste method ends in a new line   The tr method does not

User · Answer

A pure Bash way with no eval  no subshells  no external tools  no brace expansions  i e   you can have the number to repeat in a variable    If you re given a variable n that expands to a  non-negative  number and a variable pattern  e g      n 5   pattern hello   printf -v output    s    n    output   output     pattern    echo   output  hellohellohellohellohello   You can make a function with this   repeat            1 number of patterns to repeat        2 pattern        3 output variable name     local tmp     printf -v tmp    s    1      printf -v   3    s     tmp     2       With this set     repeat 5 hello output   echo   output  hellohellohellohellohello     For this little trick we re using printf quite a lot with    -v varname  instead of printing to standard output  printf will put the content of the formatted string in variable varname     s   printf will use the argument to print the corresponding number of spaces  E g   printf    s  42 will print 42 spaces  Finally  when we have the wanted number of spaces in our variable  we use a parameter expansion to replace all the spaces by our pattern    var     pattern  will expand to the expansion of var with all the spaces replaced by the expansion of  pattern      You can also get rid of the tmp variable in the repeat function by using indirect expansion   repeat            1 number of patterns to repeat        2 pattern        3 output variable name     printf -v   3     s    1      printf -v   3    s      3     2

User · Answer

Most existing solutions all depend on  1  10  syntax support of the shell  which is bash- and zsh- specific  and doesn t work in tcsh or OpenBSD s ksh and most non-bash sh   The following should work on OS X and all  BSD systems in any shell  in fact  it can be used to generate a whole matrix of various types of decorative space     printf     0s   jot 64    fold -16                                                                         Sadly  we don t get a trailing newline  which can be fixed by an extra printf   n  after the fold     printf     0s   jot 64    fold -16   printf   n                                                                           References    http   mdoc su - printf 1 http   mdoc su - jot 1 http   mdoc su - fold 1

User · Answer

Simplest is to use this one-liner in bash   seq 10   xargs -n 1   xargs -I    echo -n       gt  echo

User · Answer

Another mean to repeat an arbitrary string n times   Pros    Works with POSIX shell  Output can be assigned to a variable  Repeats any string  Very fast even with very large repeats    Cons    Requires Gnu Core Utils s yes command       usr bin sh to repeat     repeat count 80 yes   to repeat    tr -d   n    head -c   repeat count    With an ANSI terminal and US-ASCII characters to repeat  You can use an ANSI CSI escape sequence  It is the fastest way to repeat a character      usr bin env bash  char     repeat count 80 printf   c e  db    char    repeat count    Or statically   Print a line of 80 times     printf    e 80b n   Limitations    Not all terminals understands the repeat char ANSI CSI sequence  Only US-ASCII or single-byte ISO characters can be repeated  Repeat stops at last column  so you can use a large value to fill a whole line regardless of terminal width  The repeat is only for display  Capturing output into a shell variable will not expand the repeat char ANSI CSI sequence into the repeated character

User · Answer

Here s what I use to print a line of characters across the screen in linux  based on terminal screen width  Print  quot   quot  across the screen  printf     0s    seq 1   tput cols    Explanation  Print an equal sign as many times as the given sequence  printf     0s   sequence  Use the output of a command  this is a bash feature called Command Substitution     example command   Give a sequence  I ve used 1 to 20 as an example  In the final command the tput command is used instead of 20  seq 1 20  Give the number of columns currently used in the terminal  tput cols

User · Answer

Not to pile-on  but another pure-Bash approach takes advantage of       substitution of arrays     arr   1  100     printf   s     arr

User · Answer

usr bin awk -f BEGIN     OFS         NF   100   print     Or     usr bin awk -f BEGIN     while  z    lt  100  printf         Example

User · Answer

In bash 3 0 or higher  for i in  1  100  do echo -n   done

User · Answer

I guess the original purpose of the question was to do this just with the shell s built-in commands  So for loops and printfs would be legitimate  while rep  perl  and also jot below would not  Still  the following command  jot -s     -b         COLUMNS 2    for instance  prints a window-wide line of

User · Answer

Slightly longer version  but if you have to use pure Bash for some reason  you can use a while loop with an incrementing variable  n 0  while    n -lt 100    do n    n 1    echo -n      done

User · Answer

Python is ubiquitous and works the same everywhere    python -c  import sys  print       int sys argv 1         100   Character and count are passed as separate parameters

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No easy way  But for example   seq -s  100 tr -d    digit      Or maybe a standard-conforming way   printf  100s  tr           There s also a tput rep  but as for my terminals at hand  xterm and linux  they don t seem to support it

User · Answer

Simplest is to use this one-liner in csh tcsh   printf   50s n       tr    blank

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n 5  chr  x   chr string     for    i 0   i lt  n  i      do     chr string  chr string chr done echo -n  quot  chr string quot   Works for    n integer  inclusive of zero and negetive   chr printable and white space  space and tab

User · Answer

I ve just found a seriously easy way to do this using seq   UPDATE  This works on the BSD seq that comes with OS X  YMMV with other versions  seq  -f     -s    10   Will print     10 times  like this                 -f     sets the format string to ignore the numbers and just print   for each one  -s    sets the separator to an empty string to remove the newlines that seq inserts between each number The spaces after -f and -s seem to be important    EDIT  Here it is in a handy function     repeat          seq  -f  1 -s     2  echo     Which you can call like this     repeat     10   NOTE  If you re repeating   then the quotes are important

User · Answer

for i in  1  100  do   echo -n     done echo

User · Answer

There s more than one way to do it     Using a loop    Brace expansion can be used with integer literals   for i in  1  100   do echo -n    done      A C-like loop allows the use of variables    start 1 end 100 for   i  start  i lt   end  i      do echo -n    done    Using the printf builtin   printf     0s   1  100    Specifying a precision here truncates the string to fit the specified width  0   As printf reuses the format string to consume all of the arguments  this simply prints     100 times   Using head  printf  etc  and tr   head -c 100  lt   dev zero   tr   0      printf  100s   tr

[bash] How can I repeat a character in Bash?

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