Send string to stdin

Question

Is there a way to effectively do this in bash    my bash script  lt  echo  This string will be sent to stdin     I m aware that I could pipe the output from the echo such as this   echo  This string will be piped to stdin      my bash script

User · Answer

Solution You want to  1  create stdout output in one process  like echo        and  2  redirect that output to stdin input of another process but  3  without the use of the bash pipe mechanism  Here s a solution that matches all three conditions   my bash script  lt   lt  echo  This string will be sent to stdin     The  lt  is normal input redirection for stdin  The  lt       is bash process substitution  Roughly it creates a  dev fd     file with the output of the substituting command and passes that filename in place of the  lt        resulting here for example in script  lt   dev fd 123  For details  see this answer  Comparison with other solutions  A one-line heredoc sent to stdin script  lt  lt  lt   string  only allows to send static strings  not the output of other commands   Process substitution alone  such as in diff  lt  ls  bin   lt  ls  usr bin   does not send anything to stdin  Instead  the process output is saved into a file  and its path is passed as a command line argument  For the above example  this is equivalent to diff  dev fd 10  dev fd 11  a command where diff receives no input from stdin    Use cases I like that  unlike the pipe mechanism  the  lt   lt       mechanism allows to put the command first and all input after it  as is the standard for input from command line options  However  beyond commandline aesthetics  there are some cases where a pipe mechanism cannot be used  For example  when a certain command has to be provided as argument to another command  such as in this example with sshpass

User · Answer

You can also use read like this  echo  enter your name  read name echo  name

User · Answer

aliases can and can t process piped stdin    Here we create 3 lines of output    echo -e  quot line 1 nline 2 nline 3 quot  line 1 line 2 line 3   We then pipe the output to stdin of the sed command to put them all on one line    echo -e  quot line 1 nline 2 nline 3 quot     sed -e  quot  a N    ba  s  n   g quot  line 1 line 2 line 3   If we define an alias of the same sed command    alias oline  sed -e  quot  a N    ba  s  n   g quot     We can pipe the output to the stdin of the alias and it behaves exactly the same    echo -e  quot line 1 nline 2 nline 3 quot     oline line 1 line 2 line 3   The problem arises when we try to define the alias as a function    alias oline  function  oline    sed -e  quot  a N    ba  s  n   g quot    oline    Defining the alias as a funstion breaks the pipe    echo -e  quot line 1 nline 2 nline 3 quot     oline  gt

User · Answer

cat    my bash script   Enables one to type multiple lines into a program  without that input being saved in history  nor visible in ps  Just press Ctrl   C when finished typing to end cat

User · Answer

You were close   my bash script  lt  lt  lt   This string will be sent to stdin     For multiline input  here-docs are suited    my bash script  lt  lt STDIN -o other --options line 1 line 2 STDIN   Edit To the comments    To achieve binary input  say   xxd -r -p  lt  lt BINARY   iconv -f UCS-4BE -t UTF-8    my bash script 0000 79c1 0000 306f 0000 3061 0000 3093 0000 3077 0000 3093 0000 304b 0000 3093 0000 3077 0000 3093 0000 306a 0000 8a71 0000 306b 0000 30ca 0000 30f3 0000 30bb 0000 30f3 0000 30b9 0000 3092 0000 7ffb 0000 8a33 0000 3059 0000 308b 0000 3053 0000 3068 0000 304c 0000 3067 0000 304d 0000 000a BINARY   If you substitute cat for  my bash script  or indeed drop the last pipe   this prints                                  Or  if you wanted something a little more geeky   0000000  0000 0000 bef9 0e3c 59f8 8e3c 0a71 d63c          lt Y   lt  q  lt  0000010  c6f2 0e3d 3eaa 323d 3a5e 563d 090e 7a3d       gt  2   V   z  0000020  7bdc 8e3d 2aaf a03d b67e b23d c74a c43d               J   0000030  0513 d63d 16d7 e73d a296 f93d a8a8 053e                  gt  0000040  6583 0e3e 5a5b 173e 5b30 203e 3d02 293e  e   gt Z   gt  0  gt     gt  0000050  d4d0 313e f39b 3a3e 6f63 433e 1c27 4c3e    1 gt     gt ocC gt   L gt  0000060  cde6 543e 59a2 5d3e 9259 663e 4d0c 6f3e    T gt Y   gt  Yf gt M o gt  0000070  60ba 773e cf31 803e ee83 843e 78d3 883e    w gt  1  gt     gt x   gt  0000080  5720 8d3e 766a 913e beb1 953e 1cf6 993e  W   gt vj  gt     gt     gt  0000090  7a37 9e3e c275 a23e dfb0 a63e bce8 aa3e  z7  gt  u  gt     gt     gt  00000a0  441d af3e 624e b33e 017c b73e 0ca6 bb3e  D   gt bN  gt     gt     gt  00000b0  6fcc bf3e 15ef c33e e90d c83e d728 cc3e  o   gt     gt     gt     gt  00000c0  c93f d03e ac52 d43e 6c61 d83e f36b dc3e      gt  R  gt la  gt  k  gt  00000d0  2f72 e03e 0a74 e43e 7171 e83e 506a ec3e   r  gt  t  gt qq  gt Pj  gt  00000e0  945e f03e 274e f43e f738 f83e f11e fc3e      gt  N  gt  8  gt     gt  00000f0  0000 003f 09ee 013f 89d9 033f 77c2 053f              w    0000100  caa8 073f 788c 093f 776d 0b3f be4b 0d3f      x   wm   K   0000110  4427 0f3f 0000 113f e8d5 123f f3a8 143f  D                0000120  1879 163f 4e46 183f 8d10 1a3f cad7 1b3f   y  NF           0000130  fe9b 1d3f 1f5d 1f3f 241b 213f 06d6 223f                   0000140  bb8d 243f 3a42 263f 7cf3 273f 78a1 293f       B amp      x    0000150  254c 2b3f 7bf3 2c3f 7297 2e3f 0138 303f   L      r    80  0000160  22d5 313f ca6e 333f                        1  n3    Which is the sines of the first 90 degrees in 4byte binary floats

User · Answer

You can use one-line heredoc  cat  lt  lt  lt   This is coming from the stdin    the above is the same as  cat  lt  lt EOF This is coming from the stdin EOF   or you can redirect output from a command  like  diff  lt  ls  bin   lt  ls  usr bin    or you can read as  while read line do    echo   line  done  lt  some file   or simply  echo something   read param

[bash] Send string to stdin

Solution

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Use cases

Examples related to bash

Examples related to redirect

Examples related to stdin

Examples related to io-redirection