tasks a-s

Task/Read-a-file-line-by-line/UNIX-Shell/read-a-file-line-by-line-1.sh

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+# This while loop repeats for each line of the file.
+# This loop is inside a pipeline; many shells will
+# run this loop inside a subshell.
+cat input.txt |
+while IFS= read -r line ; do
+  printf '%s\n' "$line"
+done

Task/Read-a-file-line-by-line/UNIX-Shell/read-a-file-line-by-line-2.sh

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+# This loop runs in the current shell, and can read both
+# the old standard input (fd 1) and input.txt (fd 3).
+exec 3<input.txt
+while IFS= read -r line <&3 ; do
+  printf '%s\n' "$line"
+done
+exec 3>&-

Task/Read-a-file-line-by-line/UNIX-Shell/read-a-file-line-by-line-3.sh

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+# The old Bourne Shell interprets 'IFS= read' as 'IFS= ; read'.
+# It requires extra code to restore the original value of IFS.
+exec 3<input.txt
+oldifs=$IFS
+while IFS= ; read -r line <&3 ; do
+  IFS=$oldifs
+  printf '%s\n' "$line"
+done
+IFS=$oldifs
+exec 3>&-