The function LINES()

The function <LINES interprets an EOF ('1A'x) char as end of file, thus 
returning 0 if the next character is an EOF. Because the function <CHARIN 
does not interpret EOF chars, you should not mix these functions (use 
<CHARS to get the remaining characters in a stream if using <CHARIN to 
read from the stream and use <LINES if using <LINEIN to read from the 
stream). (Source: APAR PJ19194) 

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The function <LINES always opens a file. 

You should close the file after calling <LINES or your OS/2 session will 
run out of free file handles. (see also The function CHARS()) 

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see also Checking a queue and The function LINES() in Object REXX