Created SC2013 (markdown)

SC2013.md

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+# To read lines rather than words, pipe/redirect to a 'while read' loop.
+
+### Problematic code:
+
+    for line in $(cat file | grep -v '^ *#')
+    do
+      echo "Line: $line"
+    done
+
+### Correct code:
+
+    grep -v '^ *#' < file | while IFS= read -r line
+    do
+      echo "Line: $line"
+    done
+
+or without a subshell (bash, zsh, ksh):
+
+    while IFS= read -r line
+    do
+      echo "Line: $line"
+    done < <(grep -v '^ *#' < file)
+
+### Rationale:
+
+For loops by default (subject to `$IFS`) read word by word. Additionally, glob expansion will occur.
+
+Given this text file:
+
+    foo *
+    bar
+
+The for loop will print:
+
+  Line: foo
+  Line: aardwark.jpg
+  Line: bullfrog.jpg
+  ...
+
+The while loop will print:
+
+  Line: foo *
+  Line: bar
+
+
+### Contraindications
+
+If you want to read word by word, you should still use a while read loop (e.g. with `read -a` to read words into an array).
+
+Rare reasons for ignoring this message is if you don't care because your file only contains numbers and you're not interested in good practices, or if you've set `$IFS` appropriately and also disabled globbing.