Data commit

Task/Truncate-a-file/UNIX-Shell/truncate-a-file-1.sh

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+# Truncate a file named "myfile" to 1440 kilobytes.
+ls myfile >/dev/null &&
+  dd if=/dev/null of=myfile bs=1 seek=1440k

Task/Truncate-a-file/UNIX-Shell/truncate-a-file-2.sh

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+# Truncate a file named "myfile" to 1440 kilobytes.
+truncate -s 1440k myfile

Task/Truncate-a-file/UNIX-Shell/truncate-a-file-3.sh

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+# 1. simplest one-liner
+-bash$ >file
+
+# or the more clear/verbose:
+echo -n>file
+
+# 2. checks for file as input prior to truncate:
+f="file";echo -n<$f>$f
+
+# double-check file size
+ls -1 file # it's trunc
+
+# 3. multiple files (glob)
+glob=$(ls -1 file[0-9]); for f in $glob; do echo -n<$f>$f; done
+
+
+## OUTPUT:
+# 1. one-liner
+-bash-4.2$ echo -n>bad
++ echo -n
+-bash-4.2$ ls -l bad; cat bad
++ ls -l bad
+-rw-r--r--  1 fieldsa  fieldsa  0 Dec  4 20:07 bad
++ cat bad
+-bash-4.2$
+
+# 2. checks
+-bash-4.2$ set -x; f="bad"; echo -n<$f>$f
++ f=bad
++ echo -n
+-bash: bad: No such file or directory
+
+# Try again with the shortest version: f="bad"<$f>$f
++ ls -l bad
+-rw-r--r--  1 fieldsa  fieldsa  8192 Dec  5 01:04 bad
+-bash-4.2$ f="bad" <$f>$f
++ f=bad
+-bash-4.2$ ls -l
++ ls -l
+-rw-r--r--  1 fieldsa  fieldsa       0 Dec  5 01:04 bad
+-bash-4.2$ rm bad
++ rm bad
+-bash-4.2$ f="bad" <$f>$f
++ f=bad
+-bash: bad: No such file or directory
+
+# Now a bad file exists
+-bash-4.2$ echo 'abc'>bad
++ echo abc
+-bash-4.2$ ls -l bad;cat<bad
++ ls -l bad
+-rw-r--r--  1 fieldsa  fieldsa  4 Dec  4 19:21 bad
++ cat
+abc
+
+-bash-4.2$ f="bad"; echo -n<$f>$f
++ f=bad
++ echo -n
+-bash-4.2$ ls -l bad;cat<bad;echo "_EOF_"
++ ls -l bad
+-rw-r--r--  1 fieldsa  fieldsa  0 Dec  4 19:23 bad
++ cat
++ echo _EOF_
+_EOF_
+
+-bash-4.2$ rm bad
++ rm bad
+-bash-4.2$ f="bad" <$f&&echo -n>$f
++ f=bad
+-bash: bad: No such file or directory
+
+# 4. trunc(): trunc file size # truncate at length
+-bash-4.2$ trunc() { IFS= read -N $2 b<"$1"; echo -n "$b">"$1"; }
+-bash-4.2$ echo "abcdef">bad; ls -l bad; cat bad; trunc bad 3; ls -l bad; cat bad; echo "_EOF_"
++ echo abcdef
++ ls -l bad
+-rw-r--r--  1 fieldsa  fieldsa  7 Dec  4 19:59 bad
++ cat bad
+abcdef
++ trunc bad 3
++ read -N 3 b
++ echo -n abc
++ ls -l bad
+-rw-r--r--  1 fieldsa  fieldsa  3 Dec  4 19:59 bad
++ cat bad
+abc+ echo _EOF_
+_EOF_