#] 
#] *********************
#] "$d_SysMaint"'Linux/read summary.txt'  
# www.BillHowell.ca  31May2018 initial 
# view in text editor, using constant-width font (eg courier), tabWidth = 3
Great blog examples at end of this file ... especially "...Reading from more than one file at a time..."


#24************************24


29Jul2023 augment examples

#] +-----+
#] force read from terminal, eg user input!!! or nested scripts fail!!
#]    read -p "Press [Enter] key to continue..." </dev/tty

#] +-----+
#] Multiple file reads (roster database-like) :
#] exec 7<"$p_list_nameAffils"
#] exec 8<"$p_list_passwords"
#] while read -u 9 z_email; do
#] 	read -u 7 z_nameAffil
#] 	read -u 8 z_password
#] 	echo "z_email     =  $z_email"
#] 	echo "z_nameAffil =  $z_nameAffil"
#] 	echo "z_password  =  $z_password"
#] 	echo ""
#] 	#email_compose_send 
#] done 9< "$p_list_emails" 
#] close 7
#] close 8
#] 05Feb2024 Segmentation fault - exec 681<"$pinn681" must appear before each file-loop!!
#]    see example just below (not commented) 
	# proceed to start of transcript, writing lines along way 
	exec 681<"$pinn681"
	while IFS='' read -u 681 line681; do
		if		[ 'Transcript'  ==  "$line681" ]; then  break;  fi
	done  

	# consolidate each paragraph, remove [timestamp, newLine]s lines along way 
	# notice that reads continue from line above 
	bolInn=0

	exec 681<"$pinn681"
	while IFS='' read -u 681 line681; do
		if		[ ''  ==  "$line681" ]; then 
			if  [ "$bolInn" == 1 ]; then
				echo  ' '  >>"$pout681"
				# save paragraph
				cat  "$ptmp681"  |  tr  \\n  ' '  |  sed  's| \([0-9]*:[0-9]*\) | |g'  >>"$pout681"
				rm   "$ptmp681"
				bolInn=0
				echo  ' '  >>"$pout681"
			fi
		else 
			echo  "$line681"  >>"$ptmp681"
			bolInn=1
		fi
	done


#] +-----+
#] withput pNum, exact lines, no trimming
#] IFS='' to preserve leading [spaces,tabs] (IFS = "internal field separator")
#]    while IFS='' read -r line; do
#]      printf '%s\n' "$line"
#]    done < "$file"


#] +-----+
#] file read loops - eval to expand variables!!, see "$d_bin""fileops.sh"
#] pthOptrNamL_pthNdfL_argOrderNum()
#] {  
#] 	pthOptrNamL="$1"
#] 	pthNdfL="$2"
#] 	while read -u 9 optrNam; do
#] 		while read -u 8 pthNdf; do
#] #			echo  "pthNdf=  $pthNdf"
#] 			evalStr="echo  ""$pthNdf"
#] 			pthNdfFull=$(  eval "$evalStr"  )
#] #			echo  "pthNdfFull=  $pthNdfFull"
#] 			pth_optrNam_getArgOrderNum_dout  "$pthNdfFull"  "$optrNam"  
#] 		done 8< "$pthNdfL"
#] 	done 9< "$pthOptrNamL"
#] }  


#] +-----+
#] repeat warning : 
#] force read from terminal, eg user input!!! or nested scripts fail!!
#]    read -p "Press [Enter] key to continue..." </dev/tty

#] +-----+
#] from "$d_bin""email - remove emails from text file.sh"  
#] d_remove_emails()
#] {  
#] if  [ -d  "$d_withEml" ]; then 
#] 	if  [ -d  "$d_noEmail" ]; then 
#] 		find  "$d_withEml"  -maxdepth 1  -type f -name "*"  |  sed  "s#$d_withEml##"  >"$d_temp""d_remove_emails files.txt"
#] 		while  read -u 9 line; do 
#] 			cat "$d_withEml""$line"  |  sed 's/[A-Za-z0-9._-]*@[A-Za-z0-9._-]*//g'  >"$d_noEmail""$line" 
#] 		done 9< "$d_temp""d_remove_emails files.txt"  
#] 	else  echo  "directory doesnt exist : $d_noEmail"
#] 	fi
#] else echo  "directory doesnt exist : $d_withEml"
#] fi 
#] }  

#] +-----+
#] read tab-separated-columns of text file : 
#] process_one_of_several()
#] {   
#] paperNumSearch="$1"
#] 
#] let "i = 1"
#] 
#] #]    while  IFS=$'\t' read -r paperNumber copyright authorTitle; do
#] 	if [ "$paperNumSearch" == "$paperNumber" ]; then 
#] 		colour="red"
#] 		d_paperDone="$d_paperProb"
#] 		process_file 
#] 	
#] 		colour="white"
#] 		d_paperDone="$d_list""all - copyrighted/"
#] 		process_file 
#] 
#] 		let "i += 1"
#] 		break
#] 	fi
#] done < "$p_paperSpec" 
#] 
#] rm  "$p_pdftk_logs"
#] }  


#] +-----+
#] to make the read in the loop body read from the terminal:
#] exec 3<"somefile"
#] while IFS= read -r words <&3; do
#]    read -r word1 word2 junk
#]    printf 'Got words = "%s"\n' "$words"
#]    printf 'Got word1 = "%s"\n' "$word1"
#]    printf 'Got word2 = "%s"\n' "$word2"
#] done
#] This makes the input to the first read come from the file somefile 
#] while the standard input stream of the second read will read from the terminal 
#] (or wherever the standard input stream of the script comes from).

https://unix.stackexchange.com/questions/423160/problem-using-read-command-within-while-read-loop
edited Feb 10 at 9:46
answered Feb 10 at 9:16
Kusalananda


#] +-----+
#] repeat warning : 
#] force read from terminal, eg user input!!! or nested scripts fail!!
#]    read -p "Press [Enter] key to continue..." </dev/tty


#] +-----+
#] pipe data into while on a different file descriptor
#] while read -u 9 line; do
#]    NAME=$(get_ans Name "$line")
#] done 9< list.txt
#] 
#] get_ans() {
#]     local PROMPT=$1 DEFAULT=$2 ans
#]     read -p "$PROMPT [$DEFAULT]: " ans
#]     echo "${ans:-$DEFAULT}"
#] }

https://stackoverflow.com/questions/9688371/how-to-read-from-user-within-while-loop-read-line
edited Mar 13 '12 at 17:09
answered Mar 13 '12 at 17:01
glenn jackman


************************
31May2018 Howell - author provides MANY interesting cases! 
https://stackoverflow.com/questions/1521462/looping-through-the-content-of-a-file-in-bash

#] +-----+
#] cat peptides.txt | while read line
#] do
#]    # do something with $line here
#] done
answered Oct 5 '09 at 17:54
Warren Young

#] +-----+
#] Option 2: For loop: Read file into single variable and parse.
This syntax will parse "lines" based on any white space between the tokens. This still works because the given input file lines are single work tokens. If there were more than one token per line, then this method would not work as well. Also, reading the full file into a single variable is not a good strategy for large files.

#] #!/bin/bash
#] filename='peptides.txt'
#] filelines=`cat $filename`
#] echo Start
#] for line in $filelines ; do
#]     echo $line
#] done

shareimprove this answer
edited Oct 7 '14 at 9:13
mtk
6,934105189
answered Oct 5 '09 at 18:18
Stan Graves



#] +-----+
#] repeat warning : 
#] force read from terminal, eg user input!!! or nested scripts fail!!
#]    read -p "Press [Enter] key to continue..." </dev/tty


#] +-----+
#] Reading from the output of another command, using process substitution
#] while read -r line; do
#]   # process the line
#] done < <(command ...)

This approach is better than command ... | while read -r line; do ... because the while loop here runs in the current shell rather than a subshell as in the case of the latter. See the related post A variable modified inside a while loop is not remembered.

#] +-----+
#] Reading from more than one file at a time
#] while read -u 3 -r line1 && read -u 4 -r line2; do
#]   # process the lines
#]   # note that the loop will end when we reach EOF on either of the files, because of the `&&`
#] done 3< input1.txt 4< input2.txt

#] +-----+
#] Reading a whole file into an array (Bash versions 4x and later)
#]    readarray -t my_array < my_file
#] or
#]    mapfile -t my_array < my_file
#] And then
#]    for line in "${my_array[@]}"; do
#]      # process the lines
#]    done

edited Apr 25 at 4:17
answered Jan 14 '17 at 3:30
codeforester


#] +-----+
from "$d_SysMaint"'Linux/for loops notes.txt' 
23May2018 for loops :

https://www.cyberciti.biz/faq/bash-for-loop/
#] Bash For Loop Examples
Posted on October 31, 2008in Categories BASH Shell, CentOS, Debian / Ubuntu, FreeBSD, Linux, Solaris-Unix, Suse, Ubuntu Linux, UNIX last updated December 25, 2017

#] #!/bin/bash
#] FILES="$@"
#] for f in $FILES
#] do
#]         # if .bak backup file exists, read next file
#] 	if [ -f ${f}.bak ]
#] 	then
#] 		echo "Skiping $f file..."
#] 		continue  # read next file and skip the cp command
#] 	fi
#]         # we are here means no backup file exists, just use cp command to copy file
#] 	/bin/cp $f $f.bak
#] done


#] +-----+
#] read options list ...  
https://ss64.com/bash/read.html
read		Read one line from the standard input, (or from a file) and assign the word(s) to variable name(s).
Syntax
      read [-ers] [-a aname] [-p prompt] [-t timeout]
              [-n nchars] [-d delim] [name...]
Key
   -a aname
             The words are assigned to sequential indices of the array variable aname, starting at 0.
             aname is unset before any new values are assigned.  Other name arguments are ignored.
   -d delim
             The first character of delim is used to terminate the input line, rather than newline.
   -e        If the standard input is coming from a terminal, readline is used to obtain the line.
   -n nchars
             read returns after reading nchars characters rather than waiting for a complete line of
             input.
   -p prompt
             Display prompt on standard error, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal.
   -r        Backslash  does not act as an escape character.  
				 The backslash is considered to be part of the line. 
				 In particular, a backslash-newline pair can not be used as a line continuation.
   -s        Silent mode. If input is coming from a terminal, characters are not echoed.
   -t timeout
             Cause read to time out and return failure if a complete line of input is not read
             within timeout seconds. This option has no effect if read is not reading input from
             the terminal or a pipe.
#] -u fd     Read input from file descriptor fd.
************************************

#] +-----+
#] repeat warning : 
#] force read from terminal, eg user input!!! or nested scripts fail!!
#]    read -p "Press [Enter] key to continue..." </dev/tty


# enddoc