Jan Kończak

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os_cp:redirects_pipes [2023/03/22 10:35] – [more, less] jkonczakos_cp:redirects_pipes [2026/03/24 13:33] (current) – [more, less] jkonczak
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 Name comes from //con__cat__enate//. \\ Name comes from //con__cat__enate//. \\
 ''cat'' numbers lines with the ''-n'' switch and outputs non-printable characters ''cat'' numbers lines with the ''-n'' switch and outputs non-printable characters
-as ''^//x//'', ''M-//x//'', … with the ''-v'' switch.+as ''^//x//'', ''M-//x//'', … with the ''-v'' switch((This notation corresponds to keys one would have to press to input the byte. To see all bytes (''\t'' and ''\n'' is replaced by ''X''), try: \\ ''perl -e'for(0..15){printf"\t%x_",$_};print"\n";for$l(0..15){printf"_%x",$l;for$h(0..15){$c=$h<<4|$l;$c=88 if $c==9||$c==10;printf("\t%c",$c)}print"\n"}'|cat -v'')).
  
 ''**paste** //file_1// [//file2//]...'' reads round-robin one line from each input ''**paste** //file_1// [//file2//]...'' reads round-robin one line from each input
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 <small> <small>
 +''**join** [-t //separator//] [-1 //fieldNumberInFile1//] [-2 //fieldNumberInFile2//] //file1// //file2//''
 +parses two sorted files and prints their lines joined on specified fields. 
 +
 ''**fold** [-w //width//] [//file//]...'' outputs input files (or standard input) ''**fold** [-w //width//] [//file//]...'' outputs input files (or standard input)
 forcing a line break whenever a line would exceed //width// (that defaults to 80). forcing a line break whenever a line would exceed //width// (that defaults to 80).
 \\ \\
 With the ''-s'' switch ''fold'' breaks lines on spaces (or at //width// if there are no spaces). With the ''-s'' switch ''fold'' breaks lines on spaces (or at //width// if there are no spaces).
 +
 +''**column** [-x] [//file//]...'' works just like ''cat'' if the longest line in the //file//s (or standard input) would not fit twice within the terminal width. \\ Else, it prints the input in as many columns as fit the terminal, filling column first (or, with ''-x'', rows first).
 +\\
 +''**column -t** [//file//]...'' does a completely different thing: it detects columns in input (by a separator that defaults to whitespace) and outputs the input as a table.
  
 ''**od** [-t x1]'', ''**hexdump** [-C]'', and ''**xxd**'' show binary files. ''**od** [-t x1]'', ''**hexdump** [-C]'', and ''**xxd**'' show binary files.
 </small> </small>
 +
 +++++ Examples | {{page>so:redirects:cat&inline}} ++++
  
 ~~Exercise.#~~ Print any file with ''cat''. Print two files at once with ''cat''. \\ ~~Exercise.#~~ Print any file with ''cat''. Print two files at once with ''cat''. \\
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 ==== Printing text ==== ==== Printing text ====
  
-''**echo** //text//'' outputs //text// followed by a newline (unless ''-n'' is specified). \\ +''**echo** //text//'' outputs //text// followed by a newline. \\ 
-The ''-e'' switch turns backslash escapes into corresponding characters, e.g., ''\t'' +<small> 
-becomes a tab and ''\n'' a newline (cf. manual).+''echo'' is present in almost any shell of any operating system, 
 +but there is no consensus on how to interpret switches and how to treat 
 +backslashes in the text. 
 +\\ 
 +In Bash, the  ''-n'' switch supresses the newline, and ''-e'' turns backslash 
 +escapes into corresponding characters, e.g., ''\t'' becomes a tab and ''\n'' 
 +a newline (cf. manual). 
 +</small>
  
 ''**printf** //format// [//arguments//]...'' works roughly the same as the ''printf'' function in C. ''**printf** //format// [//arguments//]...'' works roughly the same as the ''printf'' function in C.
  
 <small> <small>
-''**figlet** [//text//]'' outputs //text// or the standard input by using ascii-art font. +Here and there, the course materials make use of the following toy commands: 
 +\\ 
 +''**figlet** [//text//]'' outputs //text// or the standard input by using an ascii-art font. 
 +\\
 ''**cowsay** [//text//]'' makes a cow say the //text// (or the standard input). ''**cowsay** [//text//]'' makes a cow say the //text// (or the standard input).
 </small> </small>
  
-~~Exercise.#~~ Try ''echo -e 'foo\n\nbaz' '' \\ and ''echo -e '\n\n one \033[A \033[A two \033[B \033[B \n \033[1;31m red \033[0m' '' \\ <small>[[https://en.wikipedia.org/wiki/ANSI_escape_code|ANSI escape codes]] are well summarized [[https://gist.github.com/fnky/458719343aabd01cfb17a3a4f7296797|here]]</small>+++++ Examples | {{page>so:redirects:echo&inline}} ++++ 
 + 
 +~~Exercise.#~~ Try the commands ''echo -e 'foo\n\nbaz' '' \\ and ''echo -e '\n\n one \033[A \033[A two \033[B \033[B \n \033[1;31m red \033[0m' '' \\ <small>[[https://en.wikipedia.org/wiki/ANSI_escape_code|ANSI escape codes]] are well summarized [[https://gist.github.com/fnky/458719343aabd01cfb17a3a4f7296797|here]]</small>
  
 ~~Exercise.#~~ Try ''printf "|%4.2f|%3s|%-20s|\n|%4.2f|%3s|%-20s|\n" 3.1428 pi circumference/radius 9.8 g gravity'' ~~Exercise.#~~ Try ''printf "|%4.2f|%3s|%-20s|\n|%4.2f|%3s|%-20s|\n" 3.1428 pi circumference/radius 9.8 g gravity''
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 \\ \\
 With the ''-w'' switch, ''seq'' makes all number of equal width (e.g., ''seq -w 8 11'' outputs 08, 09, 10 and 11). With the ''-w'' switch, ''seq'' makes all number of equal width (e.g., ''seq -w 8 11'' outputs 08, 09, 10 and 11).
 +
 +++++ Examples | {{page>so:redirects:seq&inline}} ++++
  
 ~~Exercise.#~~ Generate a sequence of numbers from 1 to 15. ~~Exercise.#~~ Generate a sequence of numbers from 1 to 15.
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 ~~Exercise.#~~ Redirect standard output and the standard error of the ''find /var/spool/'' command to the same file. ~~Exercise.#~~ Redirect standard output and the standard error of the ''find /var/spool/'' command to the same file.
 +
 +++++ Examples | {{page>so:redirects:out-en&inline}} ++++
  
 === Input redirections === === Input redirections ===
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 ~~Exercise.#~~ Use ''bc'' to calculate ''sqrt(2.0000)'' in non-interactive mode and redirect its output to a file. ~~Exercise.#~~ Use ''bc'' to calculate ''sqrt(2.0000)'' in non-interactive mode and redirect its output to a file.
 +
 +++++ Examples | {{page>so:redirects:in&inline}} ++++
  
 <small> <small>
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 | ''>>'' | opens //word// for appending and replaces //file_number// with the file | | ''>>'' | opens //word// for appending and replaces //file_number// with the file |
 | ''<>'' | opens //word// for reading and writing and replaces //file_number// with the file | | ''<>'' | opens //word// for reading and writing and replaces //file_number// with the file |
-| ''<<'' | 1) creates a temporary file \\ 2) reads an input line \\ 3) if the line is //word//, go to step 6 \\ 4) if there are no quotes (a pair of ''"'' or <html><code>'</code></html>) in //word//, performs the expansion((E.g., ''$VAR'' is substituted with its value, ''`date`'' is replaced by output of the date command etc.)) on the line \\ 5) writes the line to the temporary file \\ 6) opens the temporary file for reading  \\ 7) replace //file_number// with the file \\ The command is run once this is done |+| ''<<'' | 1) creates a temporary file \\ 2) reads an input line \\ 3) if the line is //word//, goes to step 7 \\ 4) if there are no quotes (a pair of ''"'' or <html><code>'</code></html>) enclosing the //word//, performs the expansion((E.g., ''$VAR'' is substituted with its value, ''`date`'' is replaced by output of the date command etc.)) on the line \\ 5) appends the line to the temporary file \\ 6) goes to step 2 \\ 7) opens the temporary file for reading  \\ 8) replace //file_number// with the file \\ The command is run once this is done |
 | ''<<-''| same as ''<<'', but after step 2 adds a step: \\ 2a) erase all leading tab characters (''\t'') \\ warning: spaces are not erased | | ''<<-''| same as ''<<'', but after step 2 adds a step: \\ 2a) erase all leading tab characters (''\t'') \\ warning: spaces are not erased |
 | ''<<<''| warning: this is a Bash extension \\ 1) creates a temporary file \\ 2) writes //word// to it \\ 3) writes a newline to it \\ 4) opens the temporary file for reading  \\ 5) replace //file_number// with the file \\ The command is run once this is done | | ''<<<''| warning: this is a Bash extension \\ 1) creates a temporary file \\ 2) writes //word// to it \\ 3) writes a newline to it \\ 4) opens the temporary file for reading  \\ 5) replace //file_number// with the file \\ The command is run once this is done |
-| ''<&'' | if //word// is a number: duplicates a readable descriptor number //word// to the number //file_number// \\  if //word/// is ''-'': closes a descriptor number //file_number// | +| ''<&'' | if //word// is a number: duplicates a readable descriptor number //word// to the number //file_number// \\  if //word// is ''-'': closes a descriptor number //file_number// | 
-| ''>&'' | if //word// is a number: duplicates a writeable descriptor number //word// to the number //file_number//  \\  if //word/// is ''-'': closes a descriptor number //file_number// |+| ''>&'' | if //word// is a number: duplicates a writeable descriptor number //word// to the number //file_number//  \\  if //word// is ''-'': closes a descriptor number //file_number// |
 | ''&>'' | warning: this is a Bash extension \\ warning: this does not allow providing //file_number// (in fact, ''&'' is the file number) \\ opens //word// for writing, truncates it and replaces streams 1 and 2 with the file | | ''&>'' | warning: this is a Bash extension \\ warning: this does not allow providing //file_number// (in fact, ''&'' is the file number) \\ opens //word// for writing, truncates it and replaces streams 1 and 2 with the file |
 | ''&>>''| warning: this is a Bash extension \\ warning: this does not allow providing //file_number// (in fact, ''&'' is the file number) \\ opens //word// for appending and replaces streams 1 and 2 with the file | | ''&>>''| warning: this is a Bash extension \\ warning: this does not allow providing //file_number// (in fact, ''&'' is the file number) \\ opens //word// for appending and replaces streams 1 and 2 with the file |
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 standard output (unless you dare to face the consequences). standard output (unless you dare to face the consequences).
  
-~~Exercise.#~~ Swap standard input with standard output of the+~~Exercise.#~~ Swap standard error with standard output of the
 ''cat /etc/motd /etc/shadow'' command. Test if you did this correctly by adding ''cat /etc/motd /etc/shadow'' command. Test if you did this correctly by adding
 ''|rev'' at the end (that will put standard output backwards). ''|rev'' at the end (that will put standard output backwards).
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 ~~Exercise.#~~ Create a named pipe //p//. Redirect input of ''fold'' from //p// ~~Exercise.#~~ Create a named pipe //p//. Redirect input of ''fold'' from //p//
 in one terminal, and redirect output of ''ps -eF'' to //p// in another terminal. in one terminal, and redirect output of ''ps -eF'' to //p// in another terminal.
-\\ Then repeat the commands, running the''ps'' before the ''fold''.+\\ Then repeat the commands, running the ''ps'' before the ''fold''.
 </small> </small>
 +
 +++++ Examples | {{page>so:redirects:pipes1-en&inline}} ++++
  
 ===== Filters ===== ===== Filters =====
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 ~~Exercise.#~~ Run ''seq 25 > //file//''. Then run ''tail -f //file//'' in one ~~Exercise.#~~ Run ''seq 25 > //file//''. Then run ''tail -f //file//'' in one
 terminal and append (with output redirection) some data to //file//. terminal and append (with output redirection) some data to //file//.
 +
 +++++ Examples | {{page>so:pipes_filters:head_tail&inline}} ++++
  
 ==== grep ==== ==== grep ====
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 <small> <small>
 The ''grep'' program accepts several regular expression grammars. The ''grep'' program accepts several regular expression grammars.
-POSIX [[https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html|specifies]]+POSIX [[https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap09.html|specifies]]
 basic (default for ''grep'') and extended regular expressions (selectable with basic (default for ''grep'') and extended regular expressions (selectable with
 ''egrep'' or ''grep -E'' ). See manual for your implementation of ''grep'' for ''egrep'' or ''grep -E'' ). See manual for your implementation of ''grep'' for
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 \\ \\
 List all files containing ''ecdsa'' in ''~/.ssh''. List all files containing ''ecdsa'' in ''~/.ssh''.
 +
 +++++ Examples | {{page>so:pipes_filters:grep&inline}} ++++
  
 ==== cut ==== ==== cut ====
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 bytes (''-b //spec//'') / fields (''-f //spec//'') in each line. bytes (''-b //spec//'') / fields (''-f //spec//'') in each line.
 \\ \\
-A filed is any number of characters separated by a single-character+A field is any number of characters separated by a single-character
 delimiter (''-d //delim//'', defaults to tab). delimiter (''-d //delim//'', defaults to tab).
  
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 ''egrep '^[Ee]{2}' /usr/share/myspell/en_US.dic'' a slash and all that follows ''egrep '^[Ee]{2}' /usr/share/myspell/en_US.dic'' a slash and all that follows
 it. it.
 +
 +++++ Examples | {{page>so:pipes_filters:cut-en&inline}} ++++
  
 ==== sort ==== ==== sort ====
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 ~~Exercise.#~~ Sort the file by the second column (alphabetically) and by the third column (numerically). ~~Exercise.#~~ Sort the file by the second column (alphabetically) and by the third column (numerically).
 </small> </small>
 +
 +++++ Examples | {{page>so:pipes_filters:sort&inline}} ++++
  
 ==== wc, uniq, nl ==== ==== wc, uniq, nl ====
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 \\ \\
 Then pipe it through ''sort'' and ''uniq'' so that you see how many times each result was hit. Then pipe it through ''sort'' and ''uniq'' so that you see how many times each result was hit.
 +
 +++++ Examples | {{page>so:pipes_filters:wc_uniq&inline}} ++++
  
 <small> <small>
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   * to squeeze all spaces   * to squeeze all spaces
   * remove all the letters ''rwx''   * remove all the letters ''rwx''
 +
 +++++ Examples | {{page>so:pipes_filters:tr-en&inline}} ++++
  
 <small> <small>
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 not human-readable file format. not human-readable file format.
 \\ \\
-''[[https://github.com/wofr06/lesspipe|lesspipe]]'' is the leading implementation+''[[https://lesspipe.org|lesspipe]]'' is the leading implementation
 of this feature. of this feature.
 </small> </small>
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