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Linux and Command-Line Basics

$ echo a > f.txt
$ echo b > f.txt
$ echo c >> f.txt
$ cat f.txt

When the commands above are run in order, which of the following is the content shown by the last cat?

  1. AOnly the one line c
  2. BThe two lines b and c
  3. CThe three lines a, b and c
Show answer and explanation

Answer: B. The two lines b and c

">" is a redirection that writes output to a file; if the file already exists, it is emptied before writing (overwritten). ">>" appends to the end of the file. The first line writes a, the ">" in the second line leaves only b, and the ">>" in the third line adds c after it, so f.txt contains the two lines b and c. To avoid wiping out an important file with >, bash can forbid overwriting with set -o noclobber.

  • A. ">>" appends rather than overwrites, so the b written in the second line remains.
  • B. Correct. > leaves only b, and >> appends c.
  • C. The ">" in the second line empties the file before writing, so the a from the first line does not remain.
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