Often...

More specifically, when the buffering mode is set to "line-buffered" — which is the default with interactive things like terminals.

In general, and to summarize, there are three buffering modes:

In block-buffered mode, flushing doesn't happen before the respective buffer, e.g. 4k bytes size, has filled up.

For example (block-buffered): 

$ strace -ewrite perl -E 'say "X"x99 for 1..100' >/dev/null
write(1, "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"..., 4096) = 4096
write(1, "XXX\nXXXXXXXXXXXXXXXXXXXXXXXXXXXX"..., 4096) = 4096
write(1, "XXXXXXX\nXXXXXXXXXXXXXXXXXXXXXXXX"..., 1808) = 1808

[download]

Without the redirect of stdout, i.e. when it's connected to the terminal, you'd see 100 write system calls à 100 bytes... (line-buffered)

In reply to Re^2: print inside a loop by Eliya
in thread print inside a loop by nbezzala

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