day2 learning task
[video] 6. The job control pipe, and
[Video] 7.shell variable (a)
[video] 8.shell variable (at)
[9] video environment variable profile
cat 1.txt |wc -l ; cat 1.txt |grep 'aaa'
ctrl z pause a task, such as a file in vi, press ctrl z, temporarily quit vi, then execute the command fg transferred back to the front desk.
It may be more pause. Use the jobs command to list the background command.
fg 2 is to vim aa.txt into the foreground.
jobs only valid in the current command line window.
• the PATH, the HOME, PWD, LOGNAME
• env command
• set command a lot more variables, and includes user-defined variables in
• custom variable A = 1
• Variable names rules: letters, numbers, underscores, the first not to a digital
value • Variable need to be enclosed in single quotes when special symbols
• variable accumulation
• global variables B = 2 Export
• the unset variable